(window.webpackJsonp=window.webpackJsonp||[]).push([[115],{446:function(s,t,a){"use strict";a.r(t);var n=a(3),e=Object(n.a)({},(function(){var s=this,t=s._self._c;return t("ContentSlotsDistributor",{attrs:{"slot-key":s.$parent.slotKey}},[t("h1",{attrs:{id:"arraybuffer"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#arraybuffer"}},[s._v("#")]),s._v(" ArrayBuffer")]),s._v(" "),t("p",[t("code",[s._v("ArrayBuffer")]),s._v("对象、"),t("code",[s._v("TypedArray")]),s._v("视图和"),t("code",[s._v("DataView")]),s._v("视图是 JavaScript 操作二进制数据的一个接口。这些对象早就存在，属于独立的规格（2011 年 2 月发布），ES6 将它们纳入了 ECMAScript 规格，并且增加了新的方法。它们都是以数组的语法处理二进制数据，所以统称为二进制数组。\n"),s._v("\n这个接口的原始设计目的，与 WebGL 项目有关。所谓 WebGL，就是指浏览器与显卡之间的通信接口，为了满足 JavaScript 与显卡之间大量的、实时的数据交换，它们之间的数据通信必须是二进制的，而不能是传统的文本格式。文本格式传递一个 32 位整数，两端的 JavaScript 脚本与显卡都要进行格式转化，将非常耗时。这时要是存在一种机制，可以像 C 语言那样，直接操作字节，将 4 个字节的 32 位整数，以二进制形式原封不动地送入显卡，脚本的性能就会大幅提升。")]),s._v(" "),t("p",[s._v("二进制数组就是在这种背景下诞生的。它很像 C 语言的数组，允许开发者以数组下标的形式，直接操作内存，大大增强了 JavaScript 处理二进制数据的能力，使得开发者有可能通过 JavaScript 与操作系统的原生接口进行二进制通信。")]),s._v(" "),t("p",[s._v("二进制数组由三类对象组成。")]),s._v(" "),t("p",[t("strong",[s._v("（1）"),t("code",[s._v("ArrayBuffer")]),s._v("对象")]),s._v("：代表内存之中的一段二进制数据，可以通过“视图”进行操作。“视图”部署了数组接口，这意味着，可以用数组的方法操作内存。")]),s._v(" "),t("p",[t("strong",[s._v("（2）"),t("code",[s._v("TypedArray")]),s._v("视图")]),s._v("：共包括 9 种类型的视图，比如"),t("code",[s._v("Uint8Array")]),s._v("（无符号 8 位整数）数组视图, "),t("code",[s._v("Int16Array")]),s._v("（16 位整数）数组视图, "),t("code",[s._v("Float32Array")]),s._v("（32 位浮点数）数组视图等等。")]),s._v(" "),t("p",[t("strong",[s._v("（3）"),t("code",[s._v("DataView")]),s._v("视图")]),s._v("：可以自定义复合格式的视图，比如第一个字节是 Uint8（无符号 8 位整数）、第二、三个字节是 Int16（16 位整数）、第四个字节开始是 Float32（32 位浮点数）等等，此外还可以自定义字节序。")]),s._v(" "),t("p",[s._v("简单说，"),t("code",[s._v("ArrayBuffer")]),s._v("对象代表原始的二进制数据，"),t("code",[s._v("TypedArray")]),s._v("视图用来读写简单类型的二进制数据，"),t("code",[s._v("DataView")]),s._v("视图用来读写复杂类型的二进制数据。")]),s._v(" "),t("p",[t("code",[s._v("TypedArray")]),s._v("视图支持的数据类型一共有 9 种（"),t("code",[s._v("DataView")]),s._v("视图支持除"),t("code",[s._v("Uint8C")]),s._v("以外的其他 8 种）。")]),s._v(" "),t("table",[t("thead",[t("tr",[t("th",[s._v("数据类型")]),s._v(" "),t("th",[s._v("字节长度")]),s._v(" "),t("th",[s._v("含义")]),s._v(" "),t("th",[s._v("对应的 C 语言类型")])])]),s._v(" "),t("tbody",[t("tr",[t("td",[s._v("Int8")]),s._v(" "),t("td",[s._v("1")]),s._v(" "),t("td",[s._v("8 位带符号整数")]),s._v(" "),t("td",[s._v("signed char")])]),s._v(" "),t("tr",[t("td",[s._v("Uint8")]),s._v(" "),t("td",[s._v("1")]),s._v(" "),t("td",[s._v("8 位不带符号整数")]),s._v(" "),t("td",[s._v("unsigned char")])]),s._v(" "),t("tr",[t("td",[s._v("Uint8C")]),s._v(" "),t("td",[s._v("1")]),s._v(" "),t("td",[s._v("8 位不带符号整数（自动过滤溢出）")]),s._v(" "),t("td",[s._v("unsigned char")])]),s._v(" "),t("tr",[t("td",[s._v("Int16")]),s._v(" "),t("td",[s._v("2")]),s._v(" "),t("td",[s._v("16 位带符号整数")]),s._v(" "),t("td",[s._v("short")])]),s._v(" "),t("tr",[t("td",[s._v("Uint16")]),s._v(" "),t("td",[s._v("2")]),s._v(" "),t("td",[s._v("16 位不带符号整数")]),s._v(" "),t("td",[s._v("unsigned short")])]),s._v(" "),t("tr",[t("td",[s._v("Int32")]),s._v(" "),t("td",[s._v("4")]),s._v(" "),t("td",[s._v("32 位带符号整数")]),s._v(" "),t("td",[s._v("int")])]),s._v(" "),t("tr",[t("td",[s._v("Uint32")]),s._v(" "),t("td",[s._v("4")]),s._v(" "),t("td",[s._v("32 位不带符号的整数")]),s._v(" "),t("td",[s._v("unsigned int")])]),s._v(" "),t("tr",[t("td",[s._v("Float32")]),s._v(" "),t("td",[s._v("4")]),s._v(" "),t("td",[s._v("32 位浮点数")]),s._v(" "),t("td",[s._v("float")])]),s._v(" "),t("tr",[t("td",[s._v("Float64")]),s._v(" "),t("td",[s._v("8")]),s._v(" "),t("td",[s._v("64 位浮点数")]),s._v(" "),t("td",[s._v("double")])])])]),s._v(" "),t("p",[s._v("注意，二进制数组并不是真正的数组，而是类似数组的对象。")]),s._v(" "),t("p",[s._v("很多浏览器操作的 API，用到了二进制数组操作二进制数据，下面是其中的几个。")]),s._v(" "),t("ul",[t("li",[t("a",{attrs:{href:"#canvas"}},[s._v("Canvas")])]),s._v(" "),t("li",[t("a",{attrs:{href:"#fetch-api"}},[s._v("Fetch API")])]),s._v(" "),t("li",[t("a",{attrs:{href:"#file-api"}},[s._v("File API")])]),s._v(" "),t("li",[t("a",{attrs:{href:"#websocket"}},[s._v("WebSockets")])]),s._v(" "),t("li",[t("a",{attrs:{href:"#ajax"}},[s._v("XMLHttpRequest")])])]),s._v(" "),t("h2",{attrs:{id:"arraybuffer-对象"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#arraybuffer-对象"}},[s._v("#")]),s._v(" ArrayBuffer 对象")]),s._v(" "),t("h3",{attrs:{id:"概述"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#概述"}},[s._v("#")]),s._v(" 概述")]),s._v(" "),t("p",[t("code",[s._v("ArrayBuffer")]),s._v("对象代表储存二进制数据的一段内存，它不能直接读写，只能通过视图（"),t("code",[s._v("TypedArray")]),s._v("视图和"),t("code",[s._v("DataView")]),s._v("视图)来读写，视图的作用是以指定格式解读二进制数据。")]),s._v(" "),t("p",[t("code",[s._v("ArrayBuffer")]),s._v("也是一个构造函数，可以分配一段可以存放数据的连续内存区域。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" buf "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("32")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br")])]),t("p",[s._v("上面代码生成了一段 32 字节的内存区域，每个字节的值默认都是 0。可以看到，"),t("code",[s._v("ArrayBuffer")]),s._v("构造函数的参数是所需要的内存大小（单位字节）。")]),s._v(" "),t("p",[s._v("为了读写这段内容，需要为它指定视图。"),t("code",[s._v("DataView")]),s._v("视图的创建，需要提供"),t("code",[s._v("ArrayBuffer")]),s._v("对象实例作为参数。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" buf "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("32")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" dataView "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("DataView")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buf"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\ndataView"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint8")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 0")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br")])]),t("p",[s._v("上面代码对一段 32 字节的内存，建立"),t("code",[s._v("DataView")]),s._v("视图，然后以不带符号的 8 位整数格式，从头读取 8 位二进制数据，结果得到 0，因为原始内存的"),t("code",[s._v("ArrayBuffer")]),s._v("对象，默认所有位都是 0。")]),s._v(" "),t("p",[s._v("另一种"),t("code",[s._v("TypedArray")]),s._v("视图，与"),t("code",[s._v("DataView")]),s._v("视图的一个区别是，它不是一个构造函数，而是一组构造函数，代表不同的数据格式。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" buffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("12")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" x1 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int32Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nx1"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" x2 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nx2"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v("  "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\nx1"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 2")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br")])]),t("p",[s._v("上面代码对同一段内存，分别建立两种视图：32 位带符号整数（"),t("code",[s._v("Int32Array")]),s._v("构造函数）和 8 位不带符号整数（"),t("code",[s._v("Uint8Array")]),s._v("构造函数）。由于两个视图对应的是同一段内存，一个视图修改底层内存，会影响到另一个视图。")]),s._v(" "),t("p",[t("code",[s._v("TypedArray")]),s._v("视图的构造函数，除了接受"),t("code",[s._v("ArrayBuffer")]),s._v("实例作为参数，还可以接受普通数组作为参数，直接分配内存生成底层的"),t("code",[s._v("ArrayBuffer")]),s._v("实例，并同时完成对这段内存的赋值。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" typedArray "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\ntypedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 3")]),s._v("\n\ntypedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("5")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\ntypedArray "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// [5, 1, 2]")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br")])]),t("p",[s._v("上面代码使用"),t("code",[s._v("TypedArray")]),s._v("视图的"),t("code",[s._v("Uint8Array")]),s._v("构造函数，新建一个不带符号的 8 位整数视图。可以看到，"),t("code",[s._v("Uint8Array")]),s._v("直接使用普通数组作为参数，对底层内存的赋值同时完成。")]),s._v(" "),t("h3",{attrs:{id:"arraybuffer-prototype-bytelength"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#arraybuffer-prototype-bytelength"}},[s._v("#")]),s._v(" ArrayBuffer.prototype.byteLength")]),s._v(" "),t("p",[t("code",[s._v("ArrayBuffer")]),s._v("实例的"),t("code",[s._v("byteLength")]),s._v("属性，返回所分配的内存区域的字节长度。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" buffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("32")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbuffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("byteLength\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 32")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br")])]),t("p",[s._v("如果要分配的内存区域很大，有可能分配失败（因为没有那么多的连续空余内存），所以有必要检查是否分配成功。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("if")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("byteLength "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("===")]),s._v(" n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 成功")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("else")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 失败")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br")])]),t("h3",{attrs:{id:"arraybuffer-prototype-slice"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#arraybuffer-prototype-slice"}},[s._v("#")]),s._v(" ArrayBuffer.prototype.slice()")]),s._v(" "),t("p",[t("code",[s._v("ArrayBuffer")]),s._v("实例有一个"),t("code",[s._v("slice")]),s._v("方法，允许将内存区域的一部分，拷贝生成一个新的"),t("code",[s._v("ArrayBuffer")]),s._v("对象。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" buffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("8")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" newBuffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("slice")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br")])]),t("p",[s._v("上面代码拷贝"),t("code",[s._v("buffer")]),s._v("对象的前 3 个字节（从 0 开始，到第 3 个字节前面结束），生成一个新的"),t("code",[s._v("ArrayBuffer")]),s._v("对象。"),t("code",[s._v("slice")]),s._v("方法其实包含两步，第一步是先分配一段新内存，第二步是将原来那个"),t("code",[s._v("ArrayBuffer")]),s._v("对象拷贝过去。")]),s._v(" "),t("p",[t("code",[s._v("slice")]),s._v("方法接受两个参数，第一个参数表示拷贝开始的字节序号（含该字节），第二个参数表示拷贝截止的字节序号（不含该字节）。如果省略第二个参数，则默认到原"),t("code",[s._v("ArrayBuffer")]),s._v("对象的结尾。")]),s._v(" "),t("p",[s._v("除了"),t("code",[s._v("slice")]),s._v("方法，"),t("code",[s._v("ArrayBuffer")]),s._v("对象不提供任何直接读写内存的方法，只允许在其上方建立视图，然后通过视图读写。")]),s._v(" "),t("h3",{attrs:{id:"arraybuffer-isview"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#arraybuffer-isview"}},[s._v("#")]),s._v(" ArrayBuffer.isView()")]),s._v(" "),t("p",[t("code",[s._v("ArrayBuffer")]),s._v("有一个静态方法"),t("code",[s._v("isView")]),s._v("，返回一个布尔值，表示参数是否为"),t("code",[s._v("ArrayBuffer")]),s._v("的视图实例。这个方法大致相当于判断参数，是否为"),t("code",[s._v("TypedArray")]),s._v("实例或"),t("code",[s._v("DataView")]),s._v("实例。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" buffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("8")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nArrayBuffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("isView")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// false")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" v "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int32Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nArrayBuffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("isView")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("v"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// true")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br")])]),t("h2",{attrs:{id:"typedarray-视图"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#typedarray-视图"}},[s._v("#")]),s._v(" TypedArray 视图")]),s._v(" "),t("h3",{attrs:{id:"概述-2"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#概述-2"}},[s._v("#")]),s._v(" 概述")]),s._v(" "),t("p",[t("code",[s._v("ArrayBuffer")]),s._v("对象作为内存区域，可以存放多种类型的数据。同一段内存，不同数据有不同的解读方式，这就叫做“视图”（view）。"),t("code",[s._v("ArrayBuffer")]),s._v("有两种视图，一种是"),t("code",[s._v("TypedArray")]),s._v("视图，另一种是"),t("code",[s._v("DataView")]),s._v("视图。前者的数组成员都是同一个数据类型，后者的数组成员可以是不同的数据类型。")]),s._v(" "),t("p",[s._v("目前，"),t("code",[s._v("TypedArray")]),s._v("视图一共包括 9 种类型，每一种视图都是一种构造函数。")]),s._v(" "),t("ul",[t("li",[t("strong",[t("code",[s._v("Int8Array")])]),s._v("：8 位有符号整数，长度 1 个字节。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("Uint8Array")])]),s._v("：8 位无符号整数，长度 1 个字节。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("Uint8ClampedArray")])]),s._v("：8 位无符号整数，长度 1 个字节，溢出处理不同。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("Int16Array")])]),s._v("：16 位有符号整数，长度 2 个字节。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("Uint16Array")])]),s._v("：16 位无符号整数，长度 2 个字节。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("Int32Array")])]),s._v("：32 位有符号整数，长度 4 个字节。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("Uint32Array")])]),s._v("：32 位无符号整数，长度 4 个字节。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("Float32Array")])]),s._v("：32 位浮点数，长度 4 个字节。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("Float64Array")])]),s._v("：64 位浮点数，长度 8 个字节。")])]),s._v(" "),t("p",[s._v("这 9 个构造函数生成的数组，统称为"),t("code",[s._v("TypedArray")]),s._v("视图。它们很像普通数组，都有"),t("code",[s._v("length")]),s._v("属性，都能用方括号运算符（"),t("code",[s._v("[]")]),s._v("）获取单个元素，所有数组的方法，在它们上面都能使用。普通数组与 TypedArray 数组的差异主要在以下方面。")]),s._v(" "),t("ul",[t("li",[s._v("TypedArray 数组的所有成员，都是同一种类型。")]),s._v(" "),t("li",[s._v("TypedArray 数组的成员是连续的，不会有空位。")]),s._v(" "),t("li",[s._v("TypedArray 数组成员的默认值为 0。比如，"),t("code",[s._v("new Array(10)")]),s._v("返回一个普通数组，里面没有任何成员，只是 10 个空位；"),t("code",[s._v("new Uint8Array(10)")]),s._v("返回一个 TypedArray 数组，里面 10 个成员都是 0。")]),s._v(" "),t("li",[s._v("TypedArray 数组只是一层视图，本身不储存数据，它的数据都储存在底层的"),t("code",[s._v("ArrayBuffer")]),s._v("对象之中，要获取底层对象必须使用"),t("code",[s._v("buffer")]),s._v("属性。")])]),s._v(" "),t("h3",{attrs:{id:"构造函数"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#构造函数"}},[s._v("#")]),s._v(" 构造函数")]),s._v(" "),t("p",[s._v("TypedArray 数组提供 9 种构造函数，用来生成相应类型的数组实例。")]),s._v(" "),t("p",[s._v("构造函数有多种用法。")]),s._v(" "),t("p",[t("strong",[s._v("（1）TypedArray(buffer, byteOffset=0, length?)")])]),s._v(" "),t("p",[s._v("同一个"),t("code",[s._v("ArrayBuffer")]),s._v("对象之上，可以根据不同的数据类型，建立多个视图。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 创建一个8字节的ArrayBuffer")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" b "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("8")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 创建一个指向b的Int32视图，开始于字节0，直到缓冲区的末尾")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" v1 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int32Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("b"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 创建一个指向b的Uint8视图，开始于字节2，直到缓冲区的末尾")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" v2 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("b"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 创建一个指向b的Int16视图，开始于字节2，长度为2")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" v3 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int16Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("b"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br")])]),t("p",[s._v("上面代码在一段长度为 8 个字节的内存（"),t("code",[s._v("b")]),s._v("）之上，生成了三个视图："),t("code",[s._v("v1")]),s._v("、"),t("code",[s._v("v2")]),s._v("和"),t("code",[s._v("v3")]),s._v("。")]),s._v(" "),t("p",[s._v("视图的构造函数可以接受三个参数：")]),s._v(" "),t("ul",[t("li",[s._v("第一个参数（必需）：视图对应的底层"),t("code",[s._v("ArrayBuffer")]),s._v("对象。")]),s._v(" "),t("li",[s._v("第二个参数（可选）：视图开始的字节序号，默认从 0 开始。")]),s._v(" "),t("li",[s._v("第三个参数（可选）：视图包含的数据个数，默认直到本段内存区域结束。")])]),s._v(" "),t("p",[s._v("因此，"),t("code",[s._v("v1")]),s._v("、"),t("code",[s._v("v2")]),s._v("和"),t("code",[s._v("v3")]),s._v("是重叠的："),t("code",[s._v("v1[0]")]),s._v("是一个 32 位整数，指向字节 0 ～字节 3；"),t("code",[s._v("v2[0]")]),s._v("是一个 8 位无符号整数，指向字节 2；"),t("code",[s._v("v3[0]")]),s._v("是一个 16 位整数，指向字节 2 ～字节 3。只要任何一个视图对内存有所修改，就会在另外两个视图上反应出来。")]),s._v(" "),t("p",[s._v("注意，"),t("code",[s._v("byteOffset")]),s._v("必须与所要建立的数据类型一致，否则会报错。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" buffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("8")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" i16 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int16Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Uncaught RangeError: start offset of Int16Array should be a multiple of 2")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br")])]),t("p",[s._v("上面代码中，新生成一个 8 个字节的"),t("code",[s._v("ArrayBuffer")]),s._v("对象，然后在这个对象的第一个字节，建立带符号的 16 位整数视图，结果报错。因为，带符号的 16 位整数需要两个字节，所以"),t("code",[s._v("byteOffset")]),s._v("参数必须能够被 2 整除。")]),s._v(" "),t("p",[s._v("如果想从任意字节开始解读"),t("code",[s._v("ArrayBuffer")]),s._v("对象，必须使用"),t("code",[s._v("DataView")]),s._v("视图，因为"),t("code",[s._v("TypedArray")]),s._v("视图只提供 9 种固定的解读格式。")]),s._v(" "),t("p",[t("strong",[s._v("（2）TypedArray(length)")])]),s._v(" "),t("p",[s._v("视图还可以不通过"),t("code",[s._v("ArrayBuffer")]),s._v("对象，直接分配内存而生成。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" f64a "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Float64Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("8")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nf64a"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nf64a"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("20")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nf64a"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" f64a"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" f64a"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br")])]),t("p",[s._v("上面代码生成一个 8 个成员的"),t("code",[s._v("Float64Array")]),s._v("数组（共 64 字节），然后依次对每个成员赋值。这时，视图构造函数的参数就是成员的个数。可以看到，视图数组的赋值操作与普通数组的操作毫无两样。")]),s._v(" "),t("p",[t("strong",[s._v("（3）TypedArray(typedArray)")])]),s._v(" "),t("p",[s._v("TypedArray 数组的构造函数，可以接受另一个"),t("code",[s._v("TypedArray")]),s._v("实例作为参数。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" typedArray "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("4")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br")])]),t("p",[s._v("上面代码中，"),t("code",[s._v("Int8Array")]),s._v("构造函数接受一个"),t("code",[s._v("Uint8Array")]),s._v("实例作为参数。")]),s._v(" "),t("p",[s._v("注意，此时生成的新数组，只是复制了参数数组的值，对应的底层内存是不一样的。新数组会开辟一段新的内存储存数据，不会在原数组的内存之上建立视图。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" x "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" y "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("x"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nx"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 1")]),s._v("\ny"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 1")]),s._v("\n\nx"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\ny"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 1")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br")])]),t("p",[s._v("上面代码中，数组"),t("code",[s._v("y")]),s._v("是以数组"),t("code",[s._v("x")]),s._v("为模板而生成的，当"),t("code",[s._v("x")]),s._v("变动的时候，"),t("code",[s._v("y")]),s._v("并没有变动。")]),s._v(" "),t("p",[s._v("如果想基于同一段内存，构造不同的视图，可以采用下面的写法。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" x "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" y "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("x"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nx"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 1")]),s._v("\ny"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 1")]),s._v("\n\nx"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\ny"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 2")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br")])]),t("p",[t("strong",[s._v("（4）TypedArray(arrayLikeObject)")])]),s._v(" "),t("p",[s._v("构造函数的参数也可以是一个普通数组，然后直接生成"),t("code",[s._v("TypedArray")]),s._v("实例。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" typedArray "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("4")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br")])]),t("p",[s._v("注意，这时"),t("code",[s._v("TypedArray")]),s._v("视图会重新开辟内存，不会在原数组的内存上建立视图。")]),s._v(" "),t("p",[s._v("上面代码从一个普通的数组，生成一个 8 位无符号整数的"),t("code",[s._v("TypedArray")]),s._v("实例。")]),s._v(" "),t("p",[s._v("TypedArray 数组也可以转换回普通数组。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" normalArray "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("...")]),s._v("typedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// or")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" normalArray "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("from")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("typedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// or")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" normalArray "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("prototype"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("slice")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("call")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("typedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br")])]),t("h3",{attrs:{id:"数组方法"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#数组方法"}},[s._v("#")]),s._v(" 数组方法")]),s._v(" "),t("p",[s._v("普通数组的操作方法和属性，对 TypedArray 数组完全适用。")]),s._v(" "),t("ul",[t("li",[t("code",[s._v("TypedArray.prototype.copyWithin(target, start[, end = this.length])")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.entries()")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.every(callbackfn, thisArg?)")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.fill(value, start=0, end=this.length)")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.filter(callbackfn, thisArg?)")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.find(predicate, thisArg?)")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.findIndex(predicate, thisArg?)")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.forEach(callbackfn, thisArg?)")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.indexOf(searchElement, fromIndex=0)")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.join(separator)")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.keys()")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.lastIndexOf(searchElement, fromIndex?)")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.map(callbackfn, thisArg?)")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.reduce(callbackfn, initialValue?)")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.reduceRight(callbackfn, initialValue?)")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.reverse()")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.slice(start=0, end=this.length)")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.some(callbackfn, thisArg?)")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.sort(comparefn)")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.toLocaleString(reserved1?, reserved2?)")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.toString()")])]),s._v(" "),t("li",[t("code",[s._v("TypedArray.prototype.values()")])])]),s._v(" "),t("p",[s._v("上面所有方法的用法，请参阅数组方法的介绍，这里不再重复了。")]),s._v(" "),t("p",[s._v("注意，TypedArray 数组没有"),t("code",[s._v("concat")]),s._v("方法。如果想要合并多个 TypedArray 数组，可以用下面这个函数。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("concatenate")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token parameter"}},[s._v("resultConstructor"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("...")]),s._v("arrays")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" totalLength "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" arr "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("of")]),s._v(" arrays"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    totalLength "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+=")]),s._v(" arr"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" result "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("resultConstructor")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("totalLength"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" offset "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" arr "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("of")]),s._v(" arrays"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    result"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("set")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("arr"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" offset"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    offset "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+=")]),s._v(" arr"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" result"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("concatenate")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("Uint8Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" Uint8Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("of")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" Uint8Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("of")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("4")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Uint8Array [1, 2, 3, 4]")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br"),t("span",{staticClass:"line-number"},[s._v("12")]),t("br"),t("span",{staticClass:"line-number"},[s._v("13")]),t("br"),t("span",{staticClass:"line-number"},[s._v("14")]),t("br"),t("span",{staticClass:"line-number"},[s._v("15")]),t("br"),t("span",{staticClass:"line-number"},[s._v("16")]),t("br")])]),t("p",[s._v("另外，TypedArray 数组与普通数组一样，部署了 Iterator 接口，所以可以被遍历。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" ui8 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" Uint8Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("of")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" byte "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("of")]),s._v(" ui8"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  console"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("byte"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 0")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 1")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 2")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br")])]),t("h3",{attrs:{id:"字节序"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#字节序"}},[s._v("#")]),s._v(" 字节序")]),s._v(" "),t("p",[s._v("字节序指的是数值在内存中的表示方式。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" buffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("16")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" int32View "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int32Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" i "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("<")]),s._v(" int32View"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  int32View"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),s._v("i"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" i "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("*")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br")])]),t("p",[s._v("上面代码生成一个 16 字节的"),t("code",[s._v("ArrayBuffer")]),s._v("对象，然后在它的基础上，建立了一个 32 位整数的视图。由于每个 32 位整数占据 4 个字节，所以一共可以写入 4 个整数，依次为 0，2，4，6。")]),s._v(" "),t("p",[s._v("如果在这段数据上接着建立一个 16 位整数的视图，则可以读出完全不一样的结果。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" int16View "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int16Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" i "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("<")]),s._v(" int16View"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  console"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v('"Entry "')]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" i "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token string"}},[s._v('": "')]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" int16View"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),s._v("i"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Entry 0: 0")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Entry 1: 0")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Entry 2: 2")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Entry 3: 0")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Entry 4: 4")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Entry 5: 0")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Entry 6: 6")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Entry 7: 0")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br"),t("span",{staticClass:"line-number"},[s._v("12")]),t("br"),t("span",{staticClass:"line-number"},[s._v("13")]),t("br")])]),t("p",[s._v("由于每个 16 位整数占据 2 个字节，所以整个"),t("code",[s._v("ArrayBuffer")]),s._v("对象现在分成 8 段。然后，由于 x86 体系的计算机都采用小端字节序（little endian），相对重要的字节排在后面的内存地址，相对不重要字节排在前面的内存地址，所以就得到了上面的结果。")]),s._v(" "),t("p",[s._v("比如，一个占据四个字节的 16 进制数"),t("code",[s._v("0x12345678")]),s._v("，决定其大小的最重要的字节是“12”，最不重要的是“78”。小端字节序将最不重要的字节排在前面，储存顺序就是"),t("code",[s._v("78563412")]),s._v("；大端字节序则完全相反，将最重要的字节排在前面，储存顺序就是"),t("code",[s._v("12345678")]),s._v("。目前，所有个人电脑几乎都是小端字节序，所以 TypedArray 数组内部也采用小端字节序读写数据，或者更准确的说，按照本机操作系统设定的字节序读写数据。")]),s._v(" "),t("p",[s._v("这并不意味大端字节序不重要，事实上，很多网络设备和特定的操作系统采用的是大端字节序。这就带来一个严重的问题：如果一段数据是大端字节序，TypedArray 数组将无法正确解析，因为它只能处理小端字节序！为了解决这个问题，JavaScript 引入"),t("code",[s._v("DataView")]),s._v("对象，可以设定字节序，下文会详细介绍。")]),s._v(" "),t("p",[s._v("下面是另一个例子。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 假定某段buffer包含如下字节 [0x02, 0x01, 0x03, 0x07]")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" buffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("4")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" v1 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nv1"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nv1"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nv1"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nv1"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("7")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" uInt16View "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint16Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 计算机采用小端字节序")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 所以头两个字节等于258")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("if")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("uInt16View"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("===")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("258")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  console"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'OK'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v('// "OK"')]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 赋值运算")]),s._v("\nuInt16View"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("255")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("    "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 字节变为[0xFF, 0x00, 0x03, 0x07]")]),s._v("\nuInt16View"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0xff05")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 字节变为[0x05, 0xFF, 0x03, 0x07]")]),s._v("\nuInt16View"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0x0210")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 字节变为[0x05, 0xFF, 0x10, 0x02]")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br"),t("span",{staticClass:"line-number"},[s._v("12")]),t("br"),t("span",{staticClass:"line-number"},[s._v("13")]),t("br"),t("span",{staticClass:"line-number"},[s._v("14")]),t("br"),t("span",{staticClass:"line-number"},[s._v("15")]),t("br"),t("span",{staticClass:"line-number"},[s._v("16")]),t("br"),t("span",{staticClass:"line-number"},[s._v("17")]),t("br"),t("span",{staticClass:"line-number"},[s._v("18")]),t("br"),t("span",{staticClass:"line-number"},[s._v("19")]),t("br"),t("span",{staticClass:"line-number"},[s._v("20")]),t("br")])]),t("p",[s._v("下面的函数可以用来判断，当前视图是小端字节序，还是大端字节序。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token constant"}},[s._v("BIG_ENDIAN")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("Symbol")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'BIG_ENDIAN'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token constant"}},[s._v("LITTLE_ENDIAN")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("Symbol")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'LITTLE_ENDIAN'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getPlatformEndianness")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" arr32 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" Uint32Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("of")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0x12345678")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" arr8 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("arr32"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("switch")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("arr8"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("*")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0x1000000")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("arr8"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("*")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0x10000")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("arr8"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("*")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0x100")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("arr8"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("case")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0x12345678")]),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v("\n      "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token constant"}},[s._v("BIG_ENDIAN")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("case")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0x78563412")]),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v("\n      "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token constant"}},[s._v("LITTLE_ENDIAN")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("default")]),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v("\n      "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("throw")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Error")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'Unknown endianness'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br"),t("span",{staticClass:"line-number"},[s._v("12")]),t("br"),t("span",{staticClass:"line-number"},[s._v("13")]),t("br"),t("span",{staticClass:"line-number"},[s._v("14")]),t("br"),t("span",{staticClass:"line-number"},[s._v("15")]),t("br")])]),t("p",[s._v("总之，与普通数组相比，TypedArray 数组的最大优点就是可以直接操作内存，不需要数据类型转换，所以速度快得多。")]),s._v(" "),t("h3",{attrs:{id:"bytes-per-element-属性"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#bytes-per-element-属性"}},[s._v("#")]),s._v(" BYTES_PER_ELEMENT 属性")]),s._v(" "),t("p",[s._v("每一种视图的构造函数，都有一个"),t("code",[s._v("BYTES_PER_ELEMENT")]),s._v("属性，表示这种数据类型占据的字节数。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("Int8Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token constant"}},[s._v("BYTES_PER_ELEMENT")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 1")]),s._v("\nUint8Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token constant"}},[s._v("BYTES_PER_ELEMENT")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 1")]),s._v("\nUint8ClampedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token constant"}},[s._v("BYTES_PER_ELEMENT")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 1")]),s._v("\nInt16Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token constant"}},[s._v("BYTES_PER_ELEMENT")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 2")]),s._v("\nUint16Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token constant"}},[s._v("BYTES_PER_ELEMENT")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 2")]),s._v("\nInt32Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token constant"}},[s._v("BYTES_PER_ELEMENT")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 4")]),s._v("\nUint32Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token constant"}},[s._v("BYTES_PER_ELEMENT")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 4")]),s._v("\nFloat32Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token constant"}},[s._v("BYTES_PER_ELEMENT")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 4")]),s._v("\nFloat64Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token constant"}},[s._v("BYTES_PER_ELEMENT")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 8")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br")])]),t("p",[s._v("这个属性在"),t("code",[s._v("TypedArray")]),s._v("实例上也能获取，即有"),t("code",[s._v("TypedArray.prototype.BYTES_PER_ELEMENT")]),s._v("。")]),s._v(" "),t("h3",{attrs:{id:"arraybuffer-与字符串的互相转换"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#arraybuffer-与字符串的互相转换"}},[s._v("#")]),s._v(" ArrayBuffer 与字符串的互相转换")]),s._v(" "),t("p",[t("code",[s._v("ArrayBuffer")]),s._v(" 和字符串的相互转换，使用原生 "),t("code",[s._v("TextEncoder")]),s._v(" 和 "),t("code",[s._v("TextDecoder")]),s._v(" 方法。为了便于说明用法，下面的代码都按照 TypeScript 的用法，给出了类型签名。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("/**\n * Convert ArrayBuffer/TypedArray to String via TextDecoder\n *\n * @see https://developer.mozilla.org/en-US/docs/Web/API/TextDecoder\n */")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("ab2str")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token literal-property property"}},[s._v("input")]),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" ArrayBuffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("|")]),s._v(" Uint8Array "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("|")]),s._v(" Int8Array "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("|")]),s._v(" Uint16Array "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("|")]),s._v(" Int16Array "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("|")]),s._v(" Uint32Array "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("|")]),s._v(" Int32Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token literal-property property"}},[s._v("outputEncoding")]),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" string "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'utf8'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" string "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" decoder "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("TextDecoder")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("outputEncoding"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" decoder"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("decode")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("input"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("/**\n * Convert String to ArrayBuffer via TextEncoder\n *\n * @see https://developer.mozilla.org/zh-CN/docs/Web/API/TextEncoder\n */")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("str2ab")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token parameter"}},[t("span",{pre:!0,attrs:{class:"token literal-property property"}},[s._v("input")]),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" string")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" ArrayBuffer "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" view "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("str2Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("input"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" view"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("buffer\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("/** Convert String to Uint8Array */")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("str2Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token parameter"}},[t("span",{pre:!0,attrs:{class:"token literal-property property"}},[s._v("input")]),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" string")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" Uint8Array "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" encoder "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("TextEncoder")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" view "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" encoder"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("encode")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("input"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" view\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br"),t("span",{staticClass:"line-number"},[s._v("12")]),t("br"),t("span",{staticClass:"line-number"},[s._v("13")]),t("br"),t("span",{staticClass:"line-number"},[s._v("14")]),t("br"),t("span",{staticClass:"line-number"},[s._v("15")]),t("br"),t("span",{staticClass:"line-number"},[s._v("16")]),t("br"),t("span",{staticClass:"line-number"},[s._v("17")]),t("br"),t("span",{staticClass:"line-number"},[s._v("18")]),t("br"),t("span",{staticClass:"line-number"},[s._v("19")]),t("br"),t("span",{staticClass:"line-number"},[s._v("20")]),t("br"),t("span",{staticClass:"line-number"},[s._v("21")]),t("br"),t("span",{staticClass:"line-number"},[s._v("22")]),t("br"),t("span",{staticClass:"line-number"},[s._v("23")]),t("br"),t("span",{staticClass:"line-number"},[s._v("24")]),t("br"),t("span",{staticClass:"line-number"},[s._v("25")]),t("br"),t("span",{staticClass:"line-number"},[s._v("26")]),t("br"),t("span",{staticClass:"line-number"},[s._v("27")]),t("br"),t("span",{staticClass:"line-number"},[s._v("28")]),t("br"),t("span",{staticClass:"line-number"},[s._v("29")]),t("br")])]),t("p",[s._v("上面代码中，"),t("code",[s._v("ab2str()")]),s._v("的第二个参数"),t("code",[s._v("outputEncoding")]),s._v("给出了输出编码的编码，一般保持默认值（"),t("code",[s._v("utf-8")]),s._v("），其他可选值参见"),t("a",{attrs:{href:"https://encoding.spec.whatwg.org",target:"_blank",rel:"noopener noreferrer"}},[s._v("官方文档"),t("OutboundLink")],1),s._v("或 "),t("a",{attrs:{href:"https://nodejs.org/api/util.html#util_whatwg_supported_encodings",target:"_blank",rel:"noopener noreferrer"}},[s._v("Node.js 文档"),t("OutboundLink")],1),s._v("。")]),s._v(" "),t("h3",{attrs:{id:"溢出"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#溢出"}},[s._v("#")]),s._v(" 溢出")]),s._v(" "),t("p",[s._v("不同的视图类型，所能容纳的数值范围是确定的。超出这个范围，就会出现溢出。比如，8 位视图只能容纳一个 8 位的二进制值，如果放入一个 9 位的值，就会溢出。")]),s._v(" "),t("p",[s._v("TypedArray 数组的溢出处理规则，简单来说，就是抛弃溢出的位，然后按照视图类型进行解释。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" uint8 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\nuint8"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("256")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nuint8"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 0")]),s._v("\n\nuint8"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("-")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nuint8"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 255")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br")])]),t("p",[s._v("上面代码中，"),t("code",[s._v("uint8")]),s._v("是一个 8 位视图，而 256 的二进制形式是一个 9 位的值"),t("code",[s._v("100000000")]),s._v("，这时就会发生溢出。根据规则，只会保留后 8 位，即"),t("code",[s._v("00000000")]),s._v("。"),t("code",[s._v("uint8")]),s._v("视图的解释规则是无符号的 8 位整数，所以"),t("code",[s._v("00000000")]),s._v("就是"),t("code",[s._v("0")]),s._v("。")]),s._v(" "),t("p",[s._v("负数在计算机内部采用“2 的补码”表示，也就是说，将对应的正数值进行否运算，然后加"),t("code",[s._v("1")]),s._v("。比如，"),t("code",[s._v("-1")]),s._v("对应的正值是"),t("code",[s._v("1")]),s._v("，进行否运算以后，得到"),t("code",[s._v("11111110")]),s._v("，再加上"),t("code",[s._v("1")]),s._v("就是补码形式"),t("code",[s._v("11111111")]),s._v("。"),t("code",[s._v("uint8")]),s._v("按照无符号的 8 位整数解释"),t("code",[s._v("11111111")]),s._v("，返回结果就是"),t("code",[s._v("255")]),s._v("。")]),s._v(" "),t("p",[s._v("一个简单转换规则，可以这样表示。")]),s._v(" "),t("ul",[t("li",[s._v("正向溢出（overflow）：当输入值大于当前数据类型的最大值，结果等于当前数据类型的最小值加上余值，再减去 1。")]),s._v(" "),t("li",[s._v("负向溢出（underflow）：当输入值小于当前数据类型的最小值，结果等于当前数据类型的最大值减去余值的绝对值，再加上 1。")])]),s._v(" "),t("p",[s._v("上面的“余值”就是模运算的结果，即 JavaScript 里面的"),t("code",[s._v("%")]),s._v("运算符的结果。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token number"}},[s._v("12")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("%")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("4")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 0")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("12")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("%")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("5")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 2")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br")])]),t("p",[s._v("上面代码中，12 除以 4 是没有余值的，而除以 5 会得到余值 2。")]),s._v(" "),t("p",[s._v("请看下面的例子。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" int8 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\nint8"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("128")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nint8"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// -128")]),s._v("\n\nint8"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("-")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("129")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nint8"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 127")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br")])]),t("p",[s._v("上面例子中，"),t("code",[s._v("int8")]),s._v("是一个带符号的 8 位整数视图，它的最大值是 127，最小值是-128。输入值为"),t("code",[s._v("128")]),s._v("时，相当于正向溢出"),t("code",[s._v("1")]),s._v("，根据“最小值加上余值（128 除以 127 的余值是 1），再减去 1”的规则，就会返回"),t("code",[s._v("-128")]),s._v("；输入值为"),t("code",[s._v("-129")]),s._v("时，相当于负向溢出"),t("code",[s._v("1")]),s._v("，根据“最大值减去余值的绝对值（-129 除以-128 的余值的绝对值是 1），再加上 1”的规则，就会返回"),t("code",[s._v("127")]),s._v("。")]),s._v(" "),t("p",[t("code",[s._v("Uint8ClampedArray")]),s._v("视图的溢出规则，与上面的规则不同。它规定，凡是发生正向溢出，该值一律等于当前数据类型的最大值，即 255；如果发生负向溢出，该值一律等于当前数据类型的最小值，即 0。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" uint8c "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8ClampedArray")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\nuint8c"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("256")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nuint8c"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 255")]),s._v("\n\nuint8c"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("-")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nuint8c"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 0")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br")])]),t("p",[s._v("上面例子中，"),t("code",[s._v("uint8C")]),s._v("是一个"),t("code",[s._v("Uint8ClampedArray")]),s._v("视图，正向溢出时都返回 255，负向溢出都返回 0。")]),s._v(" "),t("h3",{attrs:{id:"typedarray-prototype-buffer"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#typedarray-prototype-buffer"}},[s._v("#")]),s._v(" TypedArray.prototype.buffer")]),s._v(" "),t("p",[t("code",[s._v("TypedArray")]),s._v("实例的"),t("code",[s._v("buffer")]),s._v("属性，返回整段内存区域对应的"),t("code",[s._v("ArrayBuffer")]),s._v("对象。该属性为只读属性。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" a "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Float32Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("64")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" b "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("a"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br")])]),t("p",[s._v("上面代码的"),t("code",[s._v("a")]),s._v("视图对象和"),t("code",[s._v("b")]),s._v("视图对象，对应同一个"),t("code",[s._v("ArrayBuffer")]),s._v("对象，即同一段内存。")]),s._v(" "),t("h3",{attrs:{id:"typedarray-prototype-bytelength-typedarray-prototype-byteoffset"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#typedarray-prototype-bytelength-typedarray-prototype-byteoffset"}},[s._v("#")]),s._v(" TypedArray.prototype.byteLength，TypedArray.prototype.byteOffset")]),s._v(" "),t("p",[t("code",[s._v("byteLength")]),s._v("属性返回 TypedArray 数组占据的内存长度，单位为字节。"),t("code",[s._v("byteOffset")]),s._v("属性返回 TypedArray 数组从底层"),t("code",[s._v("ArrayBuffer")]),s._v("对象的哪个字节开始。这两个属性都是只读属性。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" b "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("8")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" v1 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int32Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("b"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" v2 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("b"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" v3 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int16Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("b"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\nv1"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("byteLength "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 8")]),s._v("\nv2"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("byteLength "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 6")]),s._v("\nv3"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("byteLength "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 4")]),s._v("\n\nv1"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("byteOffset "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 0")]),s._v("\nv2"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("byteOffset "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 2")]),s._v("\nv3"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("byteOffset "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 2")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br"),t("span",{staticClass:"line-number"},[s._v("12")]),t("br"),t("span",{staticClass:"line-number"},[s._v("13")]),t("br")])]),t("h3",{attrs:{id:"typedarray-prototype-length"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#typedarray-prototype-length"}},[s._v("#")]),s._v(" TypedArray.prototype.length")]),s._v(" "),t("p",[t("code",[s._v("length")]),s._v("属性表示 "),t("code",[s._v("TypedArray")]),s._v(" 数组含有多少个成员。注意将 "),t("code",[s._v("length")]),s._v(" 属性和 "),t("code",[s._v("byteLength")]),s._v(" 属性区分，前者是成员长度，后者是字节长度。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" a "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int16Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("8")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\na"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 8")]),s._v("\na"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("byteLength "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 16")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br")])]),t("h3",{attrs:{id:"typedarray-prototype-set"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#typedarray-prototype-set"}},[s._v("#")]),s._v(" TypedArray.prototype.set()")]),s._v(" "),t("p",[s._v("TypedArray 数组的"),t("code",[s._v("set")]),s._v("方法用于复制数组（普通数组或 TypedArray 数组），也就是将一段内容完全复制到另一段内存。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" a "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("8")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" b "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("8")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\nb"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("set")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("a"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br")])]),t("p",[s._v("上面代码复制"),t("code",[s._v("a")]),s._v("数组的内容到"),t("code",[s._v("b")]),s._v("数组，它是整段内存的复制，比一个个拷贝成员的那种复制快得多。")]),s._v(" "),t("p",[t("code",[s._v("set")]),s._v("方法还可以接受第二个参数，表示从"),t("code",[s._v("b")]),s._v("对象的哪一个成员开始复制"),t("code",[s._v("a")]),s._v("对象。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" a "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint16Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("8")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" b "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint16Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\nb"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("set")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("a"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br")])]),t("p",[s._v("上面代码的"),t("code",[s._v("b")]),s._v("数组比"),t("code",[s._v("a")]),s._v("数组多两个成员，所以从"),t("code",[s._v("b[2]")]),s._v("开始复制。")]),s._v(" "),t("h3",{attrs:{id:"typedarray-prototype-subarray"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#typedarray-prototype-subarray"}},[s._v("#")]),s._v(" TypedArray.prototype.subarray()")]),s._v(" "),t("p",[t("code",[s._v("subarray")]),s._v("方法是对于 TypedArray 数组的一部分，再建立一个新的视图。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" a "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint16Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("8")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" b "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" a"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("subarray")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\na"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("byteLength "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 16")]),s._v("\nb"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("byteLength "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 2")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br")])]),t("p",[t("code",[s._v("subarray")]),s._v("方法的第一个参数是起始的成员序号，第二个参数是结束的成员序号（不含该成员），如果省略则包含剩余的全部成员。所以，上面代码的"),t("code",[s._v("a.subarray(2,3)")]),s._v("，意味着 b 只包含"),t("code",[s._v("a[2]")]),s._v("一个成员，字节长度为 2。")]),s._v(" "),t("h3",{attrs:{id:"typedarray-prototype-slice"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#typedarray-prototype-slice"}},[s._v("#")]),s._v(" TypedArray.prototype.slice()")]),s._v(" "),t("p",[s._v("TypeArray 实例的"),t("code",[s._v("slice")]),s._v("方法，可以返回一个指定位置的新的"),t("code",[s._v("TypedArray")]),s._v("实例。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" ui8 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" Uint8Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("of")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nui8"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("slice")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("-")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Uint8Array [ 2 ]")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br")])]),t("p",[s._v("上面代码中，"),t("code",[s._v("ui8")]),s._v("是 8 位无符号整数数组视图的一个实例。它的"),t("code",[s._v("slice")]),s._v("方法可以从当前视图之中，返回一个新的视图实例。")]),s._v(" "),t("p",[t("code",[s._v("slice")]),s._v("方法的参数，表示原数组的具体位置，开始生成新数组。负值表示逆向的位置，即-1 为倒数第一个位置，-2 表示倒数第二个位置，以此类推。")]),s._v(" "),t("h3",{attrs:{id:"typedarray-of"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#typedarray-of"}},[s._v("#")]),s._v(" TypedArray.of()")]),s._v(" "),t("p",[s._v("TypedArray 数组的所有构造函数，都有一个静态方法"),t("code",[s._v("of")]),s._v("，用于将参数转为一个"),t("code",[s._v("TypedArray")]),s._v("实例。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("Float32Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("of")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0.151")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("-")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("8")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3.7")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Float32Array [ 0.151, -8, 3.7 ]")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br")])]),t("p",[s._v("下面三种方法都会生成同样一个 TypedArray 数组。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 方法一")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" tarr "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 方法二")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" tarr "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" Uint8Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("of")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 方法三")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" tarr "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\ntarr"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\ntarr"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\ntarr"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br")])]),t("h3",{attrs:{id:"typedarray-from"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#typedarray-from"}},[s._v("#")]),s._v(" TypedArray.from()")]),s._v(" "),t("p",[s._v("静态方法"),t("code",[s._v("from")]),s._v("接受一个可遍历的数据结构（比如数组）作为参数，返回一个基于这个结构的"),t("code",[s._v("TypedArray")]),s._v("实例。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("Uint16Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("from")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Uint16Array [ 0, 1, 2 ]")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br")])]),t("p",[s._v("这个方法还可以将一种"),t("code",[s._v("TypedArray")]),s._v("实例，转为另一种。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" ui16 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" Uint16Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("from")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("Uint8Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("of")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nui16 "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("instanceof")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint16Array")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// true")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br")])]),t("p",[t("code",[s._v("from")]),s._v("方法还可以接受一个函数，作为第二个参数，用来对每个元素进行遍历，功能类似"),t("code",[s._v("map")]),s._v("方法。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("Int8Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("of")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("127")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("126")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("125")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("map")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token parameter"}},[s._v("x")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=>")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("*")]),s._v(" x"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Int8Array [ -2, -4, -6 ]")]),s._v("\n\nInt16Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("from")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("Int8Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("of")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("127")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("126")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("125")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token parameter"}},[s._v("x")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=>")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("*")]),s._v(" x"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Int16Array [ 254, 252, 250 ]")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br")])]),t("p",[s._v("上面的例子中，"),t("code",[s._v("from")]),s._v("方法没有发生溢出，这说明遍历不是针对原来的 8 位整数数组。也就是说，"),t("code",[s._v("from")]),s._v("会将第一个参数指定的 TypedArray 数组，拷贝到另一段内存之中，处理之后再将结果转成指定的数组格式。")]),s._v(" "),t("h2",{attrs:{id:"复合视图"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#复合视图"}},[s._v("#")]),s._v(" 复合视图")]),s._v(" "),t("p",[s._v("由于视图的构造函数可以指定起始位置和长度，所以在同一段内存之中，可以依次存放不同类型的数据，这叫做“复合视图”。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" buffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("24")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" idView "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint32Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" usernameView "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("4")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("16")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" amountDueView "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Float32Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("20")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br")])]),t("p",[s._v("上面代码将一个 24 字节长度的"),t("code",[s._v("ArrayBuffer")]),s._v("对象，分成三个部分：")]),s._v(" "),t("ul",[t("li",[s._v("字节 0 到字节 3：1 个 32 位无符号整数")]),s._v(" "),t("li",[s._v("字节 4 到字节 19：16 个 8 位整数")]),s._v(" "),t("li",[s._v("字节 20 到字节 23：1 个 32 位浮点数")])]),s._v(" "),t("p",[s._v("这种数据结构可以用如下的 C 语言描述：")]),s._v(" "),t("div",{staticClass:"language-c line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-c"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("struct")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("someStruct")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("unsigned")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("long")]),s._v(" id"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("char")]),s._v(" username"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("16")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("float")]),s._v(" amountDue"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br")])]),t("h2",{attrs:{id:"dataview-视图"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#dataview-视图"}},[s._v("#")]),s._v(" DataView 视图")]),s._v(" "),t("p",[s._v("如果一段数据包括多种类型（比如服务器传来的 HTTP 数据），这时除了建立"),t("code",[s._v("ArrayBuffer")]),s._v("对象的复合视图以外，还可以通过"),t("code",[s._v("DataView")]),s._v("视图进行操作。")]),s._v(" "),t("p",[t("code",[s._v("DataView")]),s._v("视图提供更多操作选项，而且支持设定字节序。本来，在设计目的上，"),t("code",[s._v("ArrayBuffer")]),s._v("对象的各种"),t("code",[s._v("TypedArray")]),s._v("视图，是用来向网卡、声卡之类的本机设备传送数据，所以使用本机的字节序就可以了；而"),t("code",[s._v("DataView")]),s._v("视图的设计目的，是用来处理网络设备传来的数据，所以大端字节序或小端字节序是可以自行设定的。")]),s._v(" "),t("p",[t("code",[s._v("DataView")]),s._v("视图本身也是构造函数，接受一个"),t("code",[s._v("ArrayBuffer")]),s._v("对象作为参数，生成视图。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token function"}},[s._v("DataView")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ArrayBuffer buffer "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" 字节起始位置 "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" 长度"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br")])]),t("p",[s._v("下面是一个例子。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" buffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("24")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" dv "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("DataView")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br")])]),t("p",[t("code",[s._v("DataView")]),s._v("实例有以下属性，含义与"),t("code",[s._v("TypedArray")]),s._v("实例的同名方法相同。")]),s._v(" "),t("ul",[t("li",[t("code",[s._v("DataView.prototype.buffer")]),s._v("：返回对应的 ArrayBuffer 对象")]),s._v(" "),t("li",[t("code",[s._v("DataView.prototype.byteLength")]),s._v("：返回占据的内存字节长度")]),s._v(" "),t("li",[t("code",[s._v("DataView.prototype.byteOffset")]),s._v("：返回当前视图从对应的 ArrayBuffer 对象的哪个字节开始")])]),s._v(" "),t("p",[t("code",[s._v("DataView")]),s._v("实例提供 8 个方法读取内存。")]),s._v(" "),t("ul",[t("li",[t("strong",[t("code",[s._v("getInt8")])]),s._v("：读取 1 个字节，返回一个 8 位整数。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("getUint8")])]),s._v("：读取 1 个字节，返回一个无符号的 8 位整数。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("getInt16")])]),s._v("：读取 2 个字节，返回一个 16 位整数。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("getUint16")])]),s._v("：读取 2 个字节，返回一个无符号的 16 位整数。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("getInt32")])]),s._v("：读取 4 个字节，返回一个 32 位整数。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("getUint32")])]),s._v("：读取 4 个字节，返回一个无符号的 32 位整数。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("getFloat32")])]),s._v("：读取 4 个字节，返回一个 32 位浮点数。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("getFloat64")])]),s._v("：读取 8 个字节，返回一个 64 位浮点数。")])]),s._v(" "),t("p",[s._v("这一系列"),t("code",[s._v("get")]),s._v("方法的参数都是一个字节序号（不能是负数，否则会报错），表示从哪个字节开始读取。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" buffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("24")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" dv "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("DataView")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 从第1个字节读取一个8位无符号整数")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" v1 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" dv"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint8")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 从第2个字节读取一个16位无符号整数")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" v2 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" dv"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint16")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 从第4个字节读取一个16位无符号整数")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" v3 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" dv"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint16")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br")])]),t("p",[s._v("上面代码读取了"),t("code",[s._v("ArrayBuffer")]),s._v("对象的前 5 个字节，其中有一个 8 位整数和两个十六位整数。")]),s._v(" "),t("p",[s._v("如果一次读取两个或两个以上字节，就必须明确数据的存储方式，到底是小端字节序还是大端字节序。默认情况下，"),t("code",[s._v("DataView")]),s._v("的"),t("code",[s._v("get")]),s._v("方法使用大端字节序解读数据，如果需要使用小端字节序解读，必须在"),t("code",[s._v("get")]),s._v("方法的第二个参数指定"),t("code",[s._v("true")]),s._v("。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 小端字节序")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" v1 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" dv"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint16")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 大端字节序")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" v2 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" dv"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint16")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("false")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 大端字节序")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" v3 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" dv"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint16")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br")])]),t("p",[s._v("DataView 视图提供 8 个方法写入内存。")]),s._v(" "),t("ul",[t("li",[t("strong",[t("code",[s._v("setInt8")])]),s._v("：写入 1 个字节的 8 位整数。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("setUint8")])]),s._v("：写入 1 个字节的 8 位无符号整数。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("setInt16")])]),s._v("：写入 2 个字节的 16 位整数。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("setUint16")])]),s._v("：写入 2 个字节的 16 位无符号整数。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("setInt32")])]),s._v("：写入 4 个字节的 32 位整数。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("setUint32")])]),s._v("：写入 4 个字节的 32 位无符号整数。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("setFloat32")])]),s._v("：写入 4 个字节的 32 位浮点数。")]),s._v(" "),t("li",[t("strong",[t("code",[s._v("setFloat64")])]),s._v("：写入 8 个字节的 64 位浮点数。")])]),s._v(" "),t("p",[s._v("这一系列"),t("code",[s._v("set")]),s._v("方法，接受两个参数，第一个参数是字节序号，表示从哪个字节开始写入，第二个参数为写入的数据。对于那些写入两个或两个以上字节的方法，需要指定第三个参数，"),t("code",[s._v("false")]),s._v("或者"),t("code",[s._v("undefined")]),s._v("表示使用大端字节序写入，"),t("code",[s._v("true")]),s._v("表示使用小端字节序写入。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 在第1个字节，以大端字节序写入值为25的32位整数")]),s._v("\ndv"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("setInt32")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("25")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("false")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 在第5个字节，以大端字节序写入值为25的32位整数")]),s._v("\ndv"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("setInt32")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("4")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("25")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 在第9个字节，以小端字节序写入值为2.5的32位浮点数")]),s._v("\ndv"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("setFloat32")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("8")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2.5")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br")])]),t("p",[s._v("如果不确定正在使用的计算机的字节序，可以采用下面的判断方式。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" littleEndian "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" buffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("DataView")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("setInt16")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("256")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int16Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("===")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("256")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br")])]),t("p",[s._v("如果返回"),t("code",[s._v("true")]),s._v("，就是小端字节序；如果返回"),t("code",[s._v("false")]),s._v("，就是大端字节序。")]),s._v(" "),t("h2",{attrs:{id:"二进制数组的应用"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#二进制数组的应用"}},[s._v("#")]),s._v(" 二进制数组的应用")]),s._v(" "),t("p",[s._v("大量的 Web API 用到了"),t("code",[s._v("ArrayBuffer")]),s._v("对象和它的视图对象。")]),s._v(" "),t("h3",{attrs:{id:"ajax"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#ajax"}},[s._v("#")]),s._v(" AJAX")]),s._v(" "),t("p",[s._v("传统上，服务器通过 AJAX 操作只能返回文本数据，即"),t("code",[s._v("responseType")]),s._v("属性默认为"),t("code",[s._v("text")]),s._v("。"),t("code",[s._v("XMLHttpRequest")]),s._v("第二版"),t("code",[s._v("XHR2")]),s._v("允许服务器返回二进制数据，这时分成两种情况。如果明确知道返回的二进制数据类型，可以把返回类型（"),t("code",[s._v("responseType")]),s._v("）设为"),t("code",[s._v("arraybuffer")]),s._v("；如果不知道，就设为"),t("code",[s._v("blob")]),s._v("。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" xhr "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("XMLHttpRequest")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nxhr"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("open")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'GET'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" someUrl"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nxhr"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("responseType "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'arraybuffer'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\nxhr"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function-variable function"}},[s._v("onload")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" arrayBuffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" xhr"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("response"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// ···")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\nxhr"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("send")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br")])]),t("p",[s._v("如果知道传回来的是 32 位整数，可以像下面这样处理。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("xhr"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function-variable function"}},[s._v("onreadystatechange")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("if")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("req"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("readyState "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("===")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("4")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" arrayResponse "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" xhr"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("response"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" dataView "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("DataView")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("arrayResponse"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" ints "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint32Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("dataView"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("byteLength "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("/")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("4")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n    xhrDiv"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("style"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("backgroundColor "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token string"}},[s._v('"#00FF00"')]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    xhrDiv"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("innerText "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token string"}},[s._v('"Array is "')]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" ints"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token string"}},[s._v('"uints long"')]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br")])]),t("h3",{attrs:{id:"canvas"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#canvas"}},[s._v("#")]),s._v(" Canvas")]),s._v(" "),t("p",[s._v("网页"),t("code",[s._v("Canvas")]),s._v("元素输出的二进制像素数据，就是 TypedArray 数组。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" canvas "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" document"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getElementById")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'myCanvas'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" ctx "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" canvas"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getContext")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'2d'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" imageData "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" ctx"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getImageData")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" canvas"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("width"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" canvas"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("height"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" uint8ClampedArray "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" imageData"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("data"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br")])]),t("p",[s._v("需要注意的是，上面代码的"),t("code",[s._v("uint8ClampedArray")]),s._v("虽然是一个 TypedArray 数组，但是它的视图类型是一种针对"),t("code",[s._v("Canvas")]),s._v("元素的专有类型"),t("code",[s._v("Uint8ClampedArray")]),s._v("。这个视图类型的特点，就是专门针对颜色，把每个字节解读为无符号的 8 位整数，即只能取值 0 ～ 255，而且发生运算的时候自动过滤高位溢出。这为图像处理带来了巨大的方便。")]),s._v(" "),t("p",[s._v("举例来说，如果把像素的颜色值设为"),t("code",[s._v("Uint8Array")]),s._v("类型，那么乘以一个 gamma 值的时候，就必须这样计算：")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("u8"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),s._v("i"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" Math"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("min")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("255")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" Math"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("max")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" u8"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),s._v("i"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("*")]),s._v(" gamma"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br")])]),t("p",[s._v("因为"),t("code",[s._v("Uint8Array")]),s._v("类型对于大于 255 的运算结果（比如"),t("code",[s._v("0xFF+1")]),s._v("），会自动变为"),t("code",[s._v("0x00")]),s._v("，所以图像处理必须要像上面这样算。这样做很麻烦，而且影响性能。如果将颜色值设为"),t("code",[s._v("Uint8ClampedArray")]),s._v("类型，计算就简化许多。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("pixels"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),s._v("i"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("*=")]),s._v(" gamma"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br")])]),t("p",[t("code",[s._v("Uint8ClampedArray")]),s._v("类型确保将小于 0 的值设为 0，将大于 255 的值设为 255。注意，IE 10 不支持该类型。")]),s._v(" "),t("h3",{attrs:{id:"websocket"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#websocket"}},[s._v("#")]),s._v(" WebSocket")]),s._v(" "),t("p",[t("code",[s._v("WebSocket")]),s._v("可以通过"),t("code",[s._v("ArrayBuffer")]),s._v("，发送或接收二进制数据。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" socket "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("WebSocket")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'ws://127.0.0.1:8081'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nsocket"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("binaryType "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'arraybuffer'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Wait until socket is open")]),s._v("\nsocket"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("addEventListener")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'open'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token parameter"}},[s._v("event")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Send binary data")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" typedArray "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("4")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  socket"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("send")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("typedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Receive binary data")]),s._v("\nsocket"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("addEventListener")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'message'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token parameter"}},[s._v("event")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" arrayBuffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" event"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("data"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// ···")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br"),t("span",{staticClass:"line-number"},[s._v("12")]),t("br"),t("span",{staticClass:"line-number"},[s._v("13")]),t("br"),t("span",{staticClass:"line-number"},[s._v("14")]),t("br"),t("span",{staticClass:"line-number"},[s._v("15")]),t("br")])]),t("h3",{attrs:{id:"fetch-api"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#fetch-api"}},[s._v("#")]),s._v(" Fetch API")]),s._v(" "),t("p",[s._v("Fetch API 取回的数据，就是"),t("code",[s._v("ArrayBuffer")]),s._v("对象。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token function"}},[s._v("fetch")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("url"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("then")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token parameter"}},[s._v("response")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" response"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("arrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("then")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token parameter"}},[s._v("arrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// ...")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br")])]),t("h3",{attrs:{id:"file-api"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#file-api"}},[s._v("#")]),s._v(" File API")]),s._v(" "),t("p",[s._v("如果知道一个文件的二进制数据类型，也可以将这个文件读取为"),t("code",[s._v("ArrayBuffer")]),s._v("对象。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" fileInput "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" document"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getElementById")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'fileInput'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" file "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" fileInput"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("files"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" reader "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("FileReader")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nreader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("readAsArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("file"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nreader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function-variable function"}},[s._v("onload")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" arrayBuffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" reader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("result"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// ···")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br")])]),t("p",[s._v("下面以处理 bmp 文件为例。假定"),t("code",[s._v("file")]),s._v("变量是一个指向 bmp 文件的文件对象，首先读取文件。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" reader "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("FileReader")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nreader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("addEventListener")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v('"load"')]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" processimage"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("false")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nreader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("readAsArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("file"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br")])]),t("p",[s._v("然后，定义处理图像的回调函数：先在二进制数据之上建立一个"),t("code",[s._v("DataView")]),s._v("视图，再建立一个"),t("code",[s._v("bitmap")]),s._v("对象，用于存放处理后的数据，最后将图像展示在"),t("code",[s._v("Canvas")]),s._v("元素之中。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("processimage")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token parameter"}},[s._v("e")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" buffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" e"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("target"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("result"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" datav "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("DataView")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" bitmap "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 具体的处理步骤")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br")])]),t("p",[s._v("具体处理图像数据时，先处理 bmp 的文件头。具体每个文件头的格式和定义，请参阅有关资料。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("bitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("fileheader "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("fileheader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("bfType "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" datav"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint16")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("fileheader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("bfSize "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" datav"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint32")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("fileheader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("bfReserved1 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" datav"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint16")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("6")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("fileheader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("bfReserved2 "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" datav"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint16")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("8")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("fileheader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("bfOffBits "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" datav"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint32")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br")])]),t("p",[s._v("接着处理图像元信息部分。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("bitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("infoheader "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("infoheader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("biSize "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" datav"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint32")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("14")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("infoheader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("biWidth "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" datav"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint32")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("18")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("infoheader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("biHeight "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" datav"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint32")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("22")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("infoheader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("biPlanes "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" datav"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint16")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("26")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("infoheader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("biBitCount "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" datav"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint16")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("28")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("infoheader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("biCompression "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" datav"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint32")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("30")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("infoheader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("biSizeImage "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" datav"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint32")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("34")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("infoheader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("biXPelsPerMeter "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" datav"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint32")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("38")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("infoheader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("biYPelsPerMeter "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" datav"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint32")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("42")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("infoheader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("biClrUsed "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" datav"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint32")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("46")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("infoheader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("biClrImportant "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" datav"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("getUint32")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("50")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("true")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br"),t("span",{staticClass:"line-number"},[s._v("12")]),t("br")])]),t("p",[s._v("最后处理图像本身的像素信息。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" start "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" bitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("fileheader"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("bfOffBits"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nbitmap"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("pixels "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Uint8Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("buffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" start"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br")])]),t("p",[s._v("至此，图像文件的数据全部处理完成。下一步，可以根据需要，进行图像变形，或者转换格式，或者展示在"),t("code",[s._v("Canvas")]),s._v("网页元素之中。")]),s._v(" "),t("h2",{attrs:{id:"sharedarraybuffer"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#sharedarraybuffer"}},[s._v("#")]),s._v(" SharedArrayBuffer")]),s._v(" "),t("p",[s._v("JavaScript 是单线程的，Web worker 引入了多线程：主线程用来与用户互动，Worker 线程用来承担计算任务。每个线程的数据都是隔离的，通过"),t("code",[s._v("postMessage()")]),s._v("通信。下面是一个例子。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 主线程")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" w "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Worker")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'myworker.js'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br")])]),t("p",[s._v("上面代码中，主线程新建了一个 Worker 线程。该线程与主线程之间会有一个通信渠道，主线程通过"),t("code",[s._v("w.postMessage")]),s._v("向 Worker 线程发消息，同时通过"),t("code",[s._v("message")]),s._v("事件监听 Worker 线程的回应。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 主线程")]),s._v("\nw"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("postMessage")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'hi'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nw"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function-variable function"}},[s._v("onmessage")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token parameter"}},[s._v("ev")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  console"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ev"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("data"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br")])]),t("p",[s._v("上面代码中，主线程先发一个消息"),t("code",[s._v("hi")]),s._v("，然后在监听到 Worker 线程的回应后，就将其打印出来。")]),s._v(" "),t("p",[s._v("Worker 线程也是通过监听"),t("code",[s._v("message")]),s._v("事件，来获取主线程发来的消息，并作出反应。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Worker 线程")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token function-variable function"}},[s._v("onmessage")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token parameter"}},[s._v("ev")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  console"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ev"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("data"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("postMessage")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'ho'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br")])]),t("p",[s._v("线程之间的数据交换可以是各种格式，不仅仅是字符串，也可以是二进制数据。这种交换采用的是复制机制，即一个进程将需要分享的数据复制一份，通过"),t("code",[s._v("postMessage")]),s._v("方法交给另一个进程。如果数据量比较大，这种通信的效率显然比较低。很容易想到，这时可以留出一块内存区域，由主线程与 Worker 线程共享，两方都可以读写，那么就会大大提高效率，协作起来也会比较简单（不像"),t("code",[s._v("postMessage")]),s._v("那么麻烦）。")]),s._v(" "),t("p",[s._v("ES2017 引入"),t("a",{attrs:{href:"https://github.com/tc39/ecmascript_sharedmem/blob/master/TUTORIAL.md",target:"_blank",rel:"noopener noreferrer"}},[t("code",[s._v("SharedArrayBuffer")]),t("OutboundLink")],1),s._v("，允许 Worker 线程与主线程共享同一块内存。"),t("code",[s._v("SharedArrayBuffer")]),s._v("的 API 与"),t("code",[s._v("ArrayBuffer")]),s._v("一模一样，唯一的区别是后者无法共享数据。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 主线程")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 新建 1KB 共享内存")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" sharedBuffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("SharedArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1024")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 主线程将共享内存的地址发送出去")]),s._v("\nw"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("postMessage")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedBuffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 在共享内存上建立视图，供写入数据")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" sharedArray "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int32Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedBuffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br")])]),t("p",[s._v("上面代码中，"),t("code",[s._v("postMessage")]),s._v("方法的参数是"),t("code",[s._v("SharedArrayBuffer")]),s._v("对象。")]),s._v(" "),t("p",[s._v("Worker 线程从事件的"),t("code",[s._v("data")]),s._v("属性上面取到数据。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Worker 线程")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token function-variable function"}},[s._v("onmessage")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token parameter"}},[s._v("ev")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 主线程共享的数据，就是 1KB 的共享内存")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" sharedBuffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" ev"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("data"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 在共享内存上建立视图，方便读写")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" sharedArray "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int32Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedBuffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// ...")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br")])]),t("p",[s._v("共享内存也可以在 Worker 线程创建，发给主线程。")]),s._v(" "),t("p",[t("code",[s._v("SharedArrayBuffer")]),s._v("与"),t("code",[s._v("ArrayBuffer")]),s._v("一样，本身是无法读写的，必须在上面建立视图，然后通过视图读写。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 分配 10 万个 32 位整数占据的内存空间")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" sab "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("SharedArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("Int32Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token constant"}},[s._v("BYTES_PER_ELEMENT")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("*")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("100000")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 建立 32 位整数视图")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" ia "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int32Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sab"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// ia.length == 100000")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 新建一个质数生成器")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" primes "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("PrimeGenerator")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 将 10 万个质数，写入这段内存空间")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" i"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("<")]),s._v(" ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n  ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),s._v("i"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" primes"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("next")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 向 Worker 线程发送这段共享内存")]),s._v("\nw"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("postMessage")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br"),t("span",{staticClass:"line-number"},[s._v("12")]),t("br"),t("span",{staticClass:"line-number"},[s._v("13")]),t("br"),t("span",{staticClass:"line-number"},[s._v("14")]),t("br"),t("span",{staticClass:"line-number"},[s._v("15")]),t("br")])]),t("p",[s._v("Worker 线程收到数据后的处理如下。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Worker 线程")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token function-variable function"}},[s._v("onmessage")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("function")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token parameter"}},[s._v("ev")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  ia "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" ev"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("data"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  console"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 100000")]),s._v("\n  console"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("37")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 输出 163，因为这是第38个质数")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br")])]),t("h2",{attrs:{id:"atomics-对象"}},[t("a",{staticClass:"header-anchor",attrs:{href:"#atomics-对象"}},[s._v("#")]),s._v(" Atomics 对象")]),s._v(" "),t("p",[s._v("多线程共享内存，最大的问题就是如何防止两个线程同时修改某个地址，或者说，当一个线程修改共享内存以后，必须有一个机制让其他线程同步。SharedArrayBuffer API 提供"),t("code",[s._v("Atomics")]),s._v("对象，保证所有共享内存的操作都是“原子性”的，并且可以在所有线程内同步。")]),s._v(" "),t("p",[s._v("什么叫“原子性操作”呢？现代编程语言中，一条普通的命令被编译器处理以后，会变成多条机器指令。如果是单线程运行，这是没有问题的；多线程环境并且共享内存时，就会出问题，因为这一组机器指令的运行期间，可能会插入其他线程的指令，从而导致运行结果出错。请看下面的例子。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 主线程")]),s._v("\nia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("42")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("314159")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 原先的值 191")]),s._v("\nia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("37")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("123456")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 原先的值 163")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Worker 线程")]),s._v("\nconsole"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("37")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nconsole"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("42")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 可能的结果")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 123456")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 191")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br")])]),t("p",[s._v("上面代码中，主线程的原始顺序是先对 42 号位置赋值，再对 37 号位置赋值。但是，编译器和 CPU 为了优化，可能会改变这两个操作的执行顺序（因为它们之间互不依赖），先对 37 号位置赋值，再对 42 号位置赋值。而执行到一半的时候，Worker 线程可能就会来读取数据，导致打印出"),t("code",[s._v("123456")]),s._v("和"),t("code",[s._v("191")]),s._v("。")]),s._v(" "),t("p",[s._v("下面是另一个例子。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 主线程")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" sab "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("SharedArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("Int32Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token constant"}},[s._v("BYTES_PER_ELEMENT")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("*")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("100000")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" ia "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int32Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sab"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" i "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("<")]),s._v(" ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),s._v("i"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" primes"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("next")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 将质数放入 ia")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// worker 线程")]),s._v("\nia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("112")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 错误")]),s._v("\nAtomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("add")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("112")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 正确")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br")])]),t("p",[s._v("上面代码中，Worker 线程直接改写共享内存"),t("code",[s._v("ia[112]++")]),s._v("是不正确的。因为这行语句会被编译成多条机器指令，这些指令之间无法保证不会插入其他进程的指令。请设想如果两个线程同时"),t("code",[s._v("ia[112]++")]),s._v("，很可能它们得到的结果都是不正确的。")]),s._v(" "),t("p",[t("code",[s._v("Atomics")]),s._v("对象就是为了解决这个问题而提出，它可以保证一个操作所对应的多条机器指令，一定是作为一个整体运行的，中间不会被打断。也就是说，它所涉及的操作都可以看作是原子性的单操作，这可以避免线程竞争，提高多线程共享内存时的操作安全。所以，"),t("code",[s._v("ia[112]++")]),s._v("要改写成"),t("code",[s._v("Atomics.add(ia, 112, 1)")]),s._v("。")]),s._v(" "),t("p",[t("code",[s._v("Atomics")]),s._v("对象提供多种方法。")]),s._v(" "),t("p",[t("strong",[s._v("（1）Atomics.store()，Atomics.load()")])]),s._v(" "),t("p",[t("code",[s._v("store()")]),s._v("方法用来向共享内存写入数据，"),t("code",[s._v("load()")]),s._v("方法用来从共享内存读出数据。比起直接的读写操作，它们的好处是保证了读写操作的原子性。")]),s._v(" "),t("p",[s._v("此外，它们还用来解决一个问题：多个线程使用共享内存的某个位置作为开关（flag），一旦该位置的值变了，就执行特定操作。这时，必须保证该位置的赋值操作，一定是在它前面的所有可能会改写内存的操作结束后执行；而该位置的取值操作，一定是在它后面所有可能会读取该位置的操作开始之前执行。"),t("code",[s._v("store")]),s._v("方法和"),t("code",[s._v("load")]),s._v("方法就能做到这一点，编译器不会为了优化，而打乱机器指令的执行顺序。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("Atomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("load")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" index"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\nAtomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("store")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" index"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" value"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br")])]),t("p",[t("code",[s._v("store")]),s._v("方法接受三个参数：SharedBuffer 的视图、位置索引和值，返回"),t("code",[s._v("sharedArray[index]")]),s._v("的值。"),t("code",[s._v("load")]),s._v("方法只接受两个参数：SharedBuffer 的视图和位置索引，也是返回"),t("code",[s._v("sharedArray[index]")]),s._v("的值。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 主线程 main.js")]),s._v("\nia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("42")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("314159")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 原先的值 191")]),s._v("\nAtomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("store")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("37")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("123456")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 原先的值是 163")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Worker 线程 worker.js")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("while")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("Atomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("load")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("37")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("==")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("163")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nconsole"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("37")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 123456")]),s._v("\nconsole"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("42")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 314159")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br")])]),t("p",[s._v("上面代码中，主线程的"),t("code",[s._v("Atomics.store")]),s._v("向 42 号位置的赋值，一定是早于 37 位置的赋值。只要 37 号位置等于 163，Worker 线程就不会终止循环，而对 37 号位置和 42 号位置的取值，一定是在"),t("code",[s._v("Atomics.load")]),s._v("操作之后。")]),s._v(" "),t("p",[s._v("下面是另一个例子。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 主线程")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" worker "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Worker")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'worker.js'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" length "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" size "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" Int32Array"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token constant"}},[s._v("BYTES_PER_ELEMENT")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("*")]),s._v(" length"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 新建一段共享内存")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" sharedBuffer "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("SharedArrayBuffer")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("size"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" sharedArray "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int32Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedBuffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" i "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("<")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 向共享内存写入 10 个整数")]),s._v("\n  Atomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("store")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" i"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\nworker"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("postMessage")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedBuffer"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br"),t("span",{staticClass:"line-number"},[s._v("12")]),t("br")])]),t("p",[s._v("上面代码中，主线程用"),t("code",[s._v("Atomics.store()")]),s._v("方法写入数据。下面是 Worker 线程用"),t("code",[s._v("Atomics.load()")]),s._v("方法读取数据。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// worker.js")]),s._v("\nself"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("addEventListener")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'message'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token parameter"}},[s._v("event")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=>")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" sharedArray "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int32Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("event"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("data"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" i "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("<")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" arrayValue "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" Atomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("load")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" i"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    console"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token template-string"}},[t("span",{pre:!0,attrs:{class:"token template-punctuation string"}},[s._v("`")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("The item at array index ")]),t("span",{pre:!0,attrs:{class:"token interpolation"}},[t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("${")]),s._v("i"),t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("}")])]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v(" is ")]),t("span",{pre:!0,attrs:{class:"token interpolation"}},[t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("${")]),s._v("arrayValue"),t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("}")])]),t("span",{pre:!0,attrs:{class:"token template-punctuation string"}},[s._v("`")])]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("false")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br")])]),t("p",[t("strong",[s._v("（2）Atomics.exchange()")])]),s._v(" "),t("p",[s._v("Worker 线程如果要写入数据，可以使用上面的"),t("code",[s._v("Atomics.store()")]),s._v("方法，也可以使用"),t("code",[s._v("Atomics.exchange()")]),s._v("方法。它们的区别是，"),t("code",[s._v("Atomics.store()")]),s._v("返回写入的值，而"),t("code",[s._v("Atomics.exchange()")]),s._v("返回被替换的值。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Worker 线程")]),s._v("\nself"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("addEventListener")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'message'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token parameter"}},[s._v("event")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=>")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" sharedArray "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int32Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("event"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("data"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("let")]),s._v(" i "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("<")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i"),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("if")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("i "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("%")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("===")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n      "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" storedValue "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" Atomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("store")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" i"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n      console"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token template-string"}},[t("span",{pre:!0,attrs:{class:"token template-punctuation string"}},[s._v("`")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("The item at array index ")]),t("span",{pre:!0,attrs:{class:"token interpolation"}},[t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("${")]),s._v("i"),t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("}")])]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v(" is now ")]),t("span",{pre:!0,attrs:{class:"token interpolation"}},[t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("${")]),s._v("storedValue"),t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("}")])]),t("span",{pre:!0,attrs:{class:"token template-punctuation string"}},[s._v("`")])]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("else")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n      "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" exchangedValue "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" Atomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("exchange")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" i"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n      console"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token template-string"}},[t("span",{pre:!0,attrs:{class:"token template-punctuation string"}},[s._v("`")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("The item at array index ")]),t("span",{pre:!0,attrs:{class:"token interpolation"}},[t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("${")]),s._v("i"),t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("}")])]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v(" was ")]),t("span",{pre:!0,attrs:{class:"token interpolation"}},[t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("${")]),s._v("exchangedValue"),t("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[s._v("}")])]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v(", now 2")]),t("span",{pre:!0,attrs:{class:"token template-punctuation string"}},[s._v("`")])]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("false")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br"),t("span",{staticClass:"line-number"},[s._v("9")]),t("br"),t("span",{staticClass:"line-number"},[s._v("10")]),t("br"),t("span",{staticClass:"line-number"},[s._v("11")]),t("br"),t("span",{staticClass:"line-number"},[s._v("12")]),t("br"),t("span",{staticClass:"line-number"},[s._v("13")]),t("br")])]),t("p",[s._v("上面代码将共享内存的偶数位置的值改成"),t("code",[s._v("1")]),s._v("，奇数位置的值改成"),t("code",[s._v("2")]),s._v("。")]),s._v(" "),t("p",[t("strong",[s._v("（3）Atomics.wait()，Atomics.wake()")])]),s._v(" "),t("p",[s._v("使用"),t("code",[s._v("while")]),s._v("循环等待主线程的通知，不是很高效，如果用在主线程，就会造成卡顿，"),t("code",[s._v("Atomics")]),s._v("对象提供了"),t("code",[s._v("wait()")]),s._v("和"),t("code",[s._v("wake()")]),s._v("两个方法用于等待通知。这两个方法相当于锁内存，即在一个线程进行操作时，让其他线程休眠（建立锁），等到操作结束，再唤醒那些休眠的线程（解除锁）。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Worker 线程")]),s._v("\nself"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("addEventListener")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token string"}},[s._v("'message'")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),t("span",{pre:!0,attrs:{class:"token parameter"}},[s._v("event")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=>")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" sharedArray "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Int32Array")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("event"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("data"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" arrayIndex "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  "),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" expectedStoredValue "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("50")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  Atomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("wait")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" arrayIndex"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" expectedStoredValue"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n  console"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("Atomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("load")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" arrayIndex"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token boolean"}},[s._v("false")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br")])]),t("p",[s._v("上面代码中，"),t("code",[s._v("Atomics.wait()")]),s._v("方法等同于告诉 Worker 线程，只要满足给定条件（"),t("code",[s._v("sharedArray")]),s._v("的"),t("code",[s._v("0")]),s._v("号位置等于"),t("code",[s._v("50")]),s._v("），就在这一行 Worker 线程进入休眠。")]),s._v(" "),t("p",[s._v("主线程一旦更改了指定位置的值，就可以唤醒 Worker 线程。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 主线程")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" newArrayValue "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("100")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nAtomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("store")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" newArrayValue"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" arrayIndex "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),t("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("const")]),s._v(" queuePos "),t("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nAtomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("wake")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" arrayIndex"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" queuePos"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br")])]),t("p",[s._v("上面代码中，"),t("code",[s._v("sharedArray")]),s._v("的"),t("code",[s._v("0")]),s._v("号位置改为"),t("code",[s._v("100")]),s._v("，然后就执行"),t("code",[s._v("Atomics.wake()")]),s._v("方法，唤醒在"),t("code",[s._v("sharedArray")]),s._v("的"),t("code",[s._v("0")]),s._v("号位置休眠队列里的一个线程。")]),s._v(" "),t("p",[t("code",[s._v("Atomics.wait()")]),s._v("方法的使用格式如下。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("Atomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("wait")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" index"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" value"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" timeout"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br")])]),t("p",[s._v("它的四个参数含义如下。")]),s._v(" "),t("ul",[t("li",[s._v("sharedArray：共享内存的视图数组。")]),s._v(" "),t("li",[s._v("index：视图数据的位置（从0开始）。")]),s._v(" "),t("li",[s._v("value：该位置的预期值。一旦实际值等于预期值，就进入休眠。")]),s._v(" "),t("li",[s._v("timeout：整数，表示过了这个时间以后，就自动唤醒，单位毫秒。该参数可选，默认值是"),t("code",[s._v("Infinity")]),s._v("，即无限期的休眠，只有通过"),t("code",[s._v("Atomics.wake()")]),s._v("方法才能唤醒。")])]),s._v(" "),t("p",[t("code",[s._v("Atomics.wait()")]),s._v("的返回值是一个字符串，共有三种可能的值。如果"),t("code",[s._v("sharedArray[index]")]),s._v("不等于"),t("code",[s._v("value")]),s._v("，就返回字符串"),t("code",[s._v("not-equal")]),s._v("，否则就进入休眠。如果"),t("code",[s._v("Atomics.wake()")]),s._v("方法唤醒，就返回字符串"),t("code",[s._v("ok")]),s._v("；如果因为超时唤醒，就返回字符串"),t("code",[s._v("timed-out")]),s._v("。")]),s._v(" "),t("p",[t("code",[s._v("Atomics.wake()")]),s._v("方法的使用格式如下。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("Atomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("wake")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" index"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" count"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br")])]),t("p",[s._v("它的三个参数含义如下。")]),s._v(" "),t("ul",[t("li",[s._v("sharedArray：共享内存的视图数组。")]),s._v(" "),t("li",[s._v("index：视图数据的位置（从0开始）。")]),s._v(" "),t("li",[s._v("count：需要唤醒的 Worker 线程的数量，默认为"),t("code",[s._v("Infinity")]),s._v("。")])]),s._v(" "),t("p",[t("code",[s._v("Atomics.wake()")]),s._v("方法一旦唤醒休眠的 Worker 线程，就会让它继续往下运行。")]),s._v(" "),t("p",[s._v("请看一个例子。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 主线程")]),s._v("\nconsole"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("37")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 163")]),s._v("\nAtomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("store")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("37")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("123456")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nAtomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("wake")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("37")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n"),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// Worker 线程")]),s._v("\nAtomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("wait")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("37")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("163")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\nconsole"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("log")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("ia"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),t("span",{pre:!0,attrs:{class:"token number"}},[s._v("37")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("  "),t("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 123456")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br"),t("span",{staticClass:"line-number"},[s._v("2")]),t("br"),t("span",{staticClass:"line-number"},[s._v("3")]),t("br"),t("span",{staticClass:"line-number"},[s._v("4")]),t("br"),t("span",{staticClass:"line-number"},[s._v("5")]),t("br"),t("span",{staticClass:"line-number"},[s._v("6")]),t("br"),t("span",{staticClass:"line-number"},[s._v("7")]),t("br"),t("span",{staticClass:"line-number"},[s._v("8")]),t("br")])]),t("p",[s._v("上面代码中，视图数组"),t("code",[s._v("ia")]),s._v("的第 37 号位置，原来的值是"),t("code",[s._v("163")]),s._v("。Worker 线程使用"),t("code",[s._v("Atomics.wait()")]),s._v("方法，指定只要"),t("code",[s._v("ia[37]")]),s._v("等于"),t("code",[s._v("163")]),s._v("，就进入休眠状态。主线程使用"),t("code",[s._v("Atomics.store()")]),s._v("方法，将"),t("code",[s._v("123456")]),s._v("写入"),t("code",[s._v("ia[37]")]),s._v("，然后使用"),t("code",[s._v("Atomics.wake()")]),s._v("方法唤醒 Worker 线程。")]),s._v(" "),t("p",[s._v("另外，基于"),t("code",[s._v("wait")]),s._v("和"),t("code",[s._v("wake")]),s._v("这两个方法的锁内存实现，可以看 Lars T Hansen 的 "),t("a",{attrs:{href:"https://github.com/lars-t-hansen/js-lock-and-condition",target:"_blank",rel:"noopener noreferrer"}},[s._v("js-lock-and-condition"),t("OutboundLink")],1),s._v(" 这个库。")]),s._v(" "),t("p",[s._v("注意，浏览器的主线程不宜设置休眠，这会导致用户失去响应。而且，主线程实际上会拒绝进入休眠。")]),s._v(" "),t("p",[t("strong",[s._v("（4）运算方法")])]),s._v(" "),t("p",[s._v("共享内存上面的某些运算是不能被打断的，即不能在运算过程中，让其他线程改写内存上面的值。Atomics 对象提供了一些运算方法，防止数据被改写。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("Atomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("add")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" index"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" value"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br")])]),t("p",[t("code",[s._v("Atomics.add")]),s._v("用于将"),t("code",[s._v("value")]),s._v("加到"),t("code",[s._v("sharedArray[index]")]),s._v("，返回"),t("code",[s._v("sharedArray[index]")]),s._v("旧的值。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("Atomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("sub")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" index"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" value"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br")])]),t("p",[t("code",[s._v("Atomics.sub")]),s._v("用于将"),t("code",[s._v("value")]),s._v("从"),t("code",[s._v("sharedArray[index]")]),s._v("减去，返回"),t("code",[s._v("sharedArray[index]")]),s._v("旧的值。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("Atomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("and")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" index"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" value"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br")])]),t("p",[t("code",[s._v("Atomics.and")]),s._v("用于将"),t("code",[s._v("value")]),s._v("与"),t("code",[s._v("sharedArray[index]")]),s._v("进行位运算"),t("code",[s._v("and")]),s._v("，放入"),t("code",[s._v("sharedArray[index]")]),s._v("，并返回旧的值。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("Atomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("or")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" index"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" value"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br")])]),t("p",[t("code",[s._v("Atomics.or")]),s._v("用于将"),t("code",[s._v("value")]),s._v("与"),t("code",[s._v("sharedArray[index]")]),s._v("进行位运算"),t("code",[s._v("or")]),s._v("，放入"),t("code",[s._v("sharedArray[index]")]),s._v("，并返回旧的值。")]),s._v(" "),t("div",{staticClass:"language-javascript line-numbers-mode"},[t("pre",{pre:!0,attrs:{class:"language-javascript"}},[t("code",[s._v("Atomics"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),t("span",{pre:!0,attrs:{class:"token function"}},[s._v("xor")]),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sharedArray"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" index"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" value"),t("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("\n")])]),s._v(" "),t("div",{staticClass:"line-numbers-wrapper"},[t("span",{staticClass:"line-number"},[s._v("1")]),t("br")])]),t("p",[t("code",[s._v("Atomic.xor")]),s._v("用于将"),t("code",[s._v("vaule")]),s._v("与"),t("code",[s._v("sharedArray[index]")]),s._v("进行位运算"),t("code",[s._v("xor")]),s._v("，放入"),t("code",[s._v("sharedArray[index]")]),s._v("，并返回旧的值。")]),s._v(" "),t("p",[t("strong",[s._v("（5）其他方法")])]),s._v(" "),t("p",[t("code",[s._v("Atomics")]),s._v("对象还有以下方法。")]),s._v(" "),t("ul",[t("li",[t("code",[s._v("Atomics.compareExchange(sharedArray, index, oldval, newval)")]),s._v("：如果"),t("code",[s._v("sharedArray[index]")]),s._v("等于"),t("code",[s._v("oldval")]),s._v("，就写入"),t("code",[s._v("newval")]),s._v("，返回"),t("code",[s._v("oldval")]),s._v("。")]),s._v(" "),t("li",[t("code",[s._v("Atomics.isLockFree(size)")]),s._v("：返回一个布尔值，表示"),t("code",[s._v("Atomics")]),s._v("对象是否可以处理某个"),t("code",[s._v("size")]),s._v("的内存锁定。如果返回"),t("code",[s._v("false")]),s._v("，应用程序就需要自己来实现锁定。")])]),s._v(" "),t("p",[t("code",[s._v("Atomics.compareExchange")]),s._v("的一个用途是，从 SharedArrayBuffer 读取一个值，然后对该值进行某个操作，操作结束以后，检查一下 SharedArrayBuffer 里面原来那个值是否发生变化（即被其他线程改写过）。如果没有改写过，就将它写回原来的位置，否则读取新的值，再重头进行一次操作。")])])}),[],!1,null,null,null);t.default=e.exports}}]);