| 1 |
- (window.webpackJsonp=window.webpackJsonp||[]).push([[98],{428: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:"对象的新增方法"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#对象的新增方法"}},[t._v("#")]),t._v(" 对象的新增方法")]),t._v(" "),s("p",[t._v("本章介绍 Object 对象的新增方法。")]),t._v(" "),s("h2",{attrs:{id:"object-is"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#object-is"}},[t._v("#")]),t._v(" Object.is()")]),t._v(" "),s("p",[t._v("ES5 比较两个值是否相等，只有两个运算符：相等运算符（"),s("code",[t._v("==")]),t._v("）和严格相等运算符（"),s("code",[t._v("===")]),t._v("）。它们都有缺点，前者会自动转换数据类型，后者的"),s("code",[t._v("NaN")]),t._v("不等于自身，以及"),s("code",[t._v("+0")]),t._v("等于"),s("code",[t._v("-0")]),t._v("。JavaScript 缺乏一种运算，在所有环境中，只要两个值是一样的，它们就应该相等。")]),t._v(" "),s("p",[t._v("ES6 提出“Same-value equality”（同值相等）算法，用来解决这个问题。"),s("code",[t._v("Object.is")]),t._v("就是部署这个算法的新方法。它用来比较两个值是否严格相等，与严格比较运算符（===）的行为基本一致。\n")]),t._v(" "),s("div",{staticClass:"language-javascript line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-javascript"}},[s("code",[t._v("Object"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("is")]),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("'foo'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// true")]),t._v("\nObject"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("is")]),s("span",{pre:!0,attrs:{class:"token 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"),s("h3",{attrs:{id:"基本用法"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#基本用法"}},[t._v("#")]),t._v(" 基本用法")]),t._v(" "),s("p",[s("code",[t._v("Object.assign")]),t._v("方法用于对象的合并，将源对象（source）的所有可枚举属性，复制到目标对象（target）。")]),t._v(" "),s("div",{staticClass:"language-javascript line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-javascript"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" target "),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("a")]),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(";")]),t._v("\n\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("span",{staticClass:"line-number"},[t._v("7")]),s("br")])]),s("p",[s("code",[t._v("Object.assign")]),t._v("方法的第一个参数是目标对象，后面的参数都是源对象。")]),t._v(" "),s("p",[t._v("注意，如果目标对象与源对象有同名属性，或多个源对象有同名属性，则后面的属性会覆盖前面的属性。")]),t._v(" "),s("div",{staticClass:"language-javascript line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-javascript"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" target "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" 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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("\n\nObject"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("assign")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("target"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" source1"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" source2"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\ntarget "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// {a:1, b:2, c:3}")]),t._v("\n")])]),t._v(" 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"),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'c'")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nObject"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("values")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("obj"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// ["b", "c", "a"]')]),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，属性名为数值的属性，是按照数值大小，从小到大遍历的，因此返回的顺序是"),s("code",[t._v("b")]),t._v("、"),s("code",[t._v("c")]),t._v("、"),s("code",[t._v("a")]),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("p",[t._v("上面代码中，"),s("code",[t._v("Object.create")]),t._v("方法的第二个参数添加的对象属性（属性"),s("code",[t._v("p")]),t._v("），如果不显式声明，默认是不可遍历的，因为"),s("code",[t._v("p")]),t._v("的属性描述对象的"),s("code",[t._v("enumerable")]),t._v("默认是"),s("code",[t._v("false")]),t._v("，"),s("code",[t._v("Object.values")]),t._v("不会返回这个属性。只要把"),s("code",[t._v("enumerable")]),t._v("改成"),s("code",[t._v("true")]),t._v("，"),s("code",[t._v("Object.values")]),t._v("就会返回属性"),s("code",[t._v("p")]),t._v("的值。")]),t._v(" "),s("div",{staticClass:"language-javascript line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-javascript"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" obj "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" Object"),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("Object.values")]),t._v("会过滤属性名为 Symbol 值的属性。")]),t._v(" "),s("div",{staticClass:"language-javascript line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-javascript"}},[s("code",[t._v("Object"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("values")]),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 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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("p",[t._v("该方法的一个用处是配合"),s("code",[t._v("URLSearchParams")]),t._v("对象，将查询字符串转为对象。")]),t._v(" "),s("div",{staticClass:"language-javascript line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-javascript"}},[s("code",[t._v("Object"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("fromEntries")]),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("URLSearchParams")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'foo=bar&baz=qux'")]),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('// { foo: "bar", baz: "qux" }')]),t._v("\n")])]),t._v(" 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