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92.873706ba.js

92.873706ba.js 68 KB
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1 
  1. (window.webpackJsonp=window.webpackJsonp||[]).push([[92],{421: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:"字符串的新增方法"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#字符串的新增方法"}},[t._v("#")]),t._v(" 字符串的新增方法")]),t._v(" "),s("p",[t._v("本章介绍字符串对象的新增方法。")]),t._v(" "),s("h2",{attrs:{id:"string-fromcodepoint"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#string-fromcodepoint"}},[t._v("#")]),t._v(" String.fromCodePoint()")]),t._v(" "),s("p",[t._v("ES5 提供"),s("code",[t._v("String.fromCharCode()")]),t._v("方法，用于从 Unicode 码点返回对应字符，但是这个方法不能识别码点大于"),s("code",[t._v("0xFFFF")]),t._v("的字符。")]),t._v(" "),s("div",{staticClass:"language-javascript line-numbers-mode"},[s("pre",{pre:!0,attrs:{class:"language-javascript"}},[s("code",[t._v("String"),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("p",[t._v("上面代码中，汉字“𠮷”（注意，这个字不是“吉祥”的“吉”）的码点是"),s("code",[t._v("0x20BB7")]),t._v("，UTF-16 编码为"),s("code",[t._v("0xD842 0xDFB7")]),t._v("（十进制为"),s("code",[t._v("55362 57271")]),t._v("），需要"),s("code",[t._v("4")]),t._v("个字节储存。对于这种"),s("code",[t._v("4")]),t._v("个字节的字符，JavaScript 不能正确处理，字符串长度会误判为"),s("code",[t._v("2")]),t._v("，而且"),s("code",[t._v("charAt()")]),t._v("方法无法读取整个字符，"),s("code",[t._v("charCodeAt()")]),t._v("方法只能分别返回前两个字节和后两个字节的值。")]),t._v(" "),s("p",[t._v("ES6 提供了"),s("code",[t._v("codePointAt()")]),t._v("方法，能够正确处理 4 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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",[s("code",[t._v("codePointAt()")]),t._v("方法是测试一个字符由两个字节还是由四个字节组成的最简单方法。")]),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("function")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("is32Bit")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("c")]),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("span",{staticClass:"line-number"},[t._v("6")]),s("br")])]),s("h2",{attrs:{id:"实例方法-normalize"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#实例方法-normalize"}},[t._v("#")]),t._v(" 实例方法：normalize()")]),t._v(" "),s("p",[t._v("许多欧洲语言有语调符号和重音符号。为了表示它们，Unicode 提供了两种方法。一种是直接提供带重音符号的字符，比如"),s("code",[t._v("Ǒ")]),t._v("（\\u01D1）。另一种是提供合成符号（combining character），即原字符与重音符号的合成，两个字符合成一个字符，比如"),s("code",[t._v("O")]),t._v("（\\u004F）和"),s("code",[t._v("ˇ")]),t._v("（\\u030C）合成"),s("code",[t._v("Ǒ")]),t._v("（\\u004F\\u030C）。")]),t._v(" "),s("p",[t._v("这两种表示方法，在视觉和语义上都等价，但是 JavaScript 不能识别。")]),t._v(" "),s("div",{staticClass:"language-javascript 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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("上面代码表示，JavaScript 将合成字符视为两个字符，导致两种表示方法不相等。")]),t._v(" "),s("p",[t._v("ES6 提供字符串实例的"),s("code",[t._v("normalize()")]),t._v("方法，用来将字符的不同表示方法统一为同样的形式，这称为 Unicode 正规化。")]),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 string"}},[t._v("'\\u01D1'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("normalize")]),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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punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[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("参数"),s("code",[t._v("NaN")]),t._v("等同于 0。")]),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 string"}},[t._v("'na'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("repeat")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("NaN")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[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"),s("code",[t._v("repeat")]),t._v("的参数是字符串，则会先转换成数字。")]),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 string"}},[t._v("'na'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("repeat")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'na'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// ""')]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'na'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("repeat")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'3'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "nanana"')]),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("h2",{attrs:{id:"实例方法-padstart-补全头部-padend-补全末尾"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#实例方法-padstart-补全头部-padend-补全末尾"}},[t._v("#")]),t._v(" 实例方法：padStart() 补全头部，padEnd() 补全末尾")]),t._v(" "),s("p",[t._v("ES2017 引入了字符串补全长度的功能。如果某个字符串不够指定长度，会在头部或尾部补全。"),s("code",[t._v("padStart()")]),t._v("用于"),s("strong",[t._v("头部补全")]),t._v("，"),s("code",[t._v("padEnd()")]),t._v("用于"),s("strong",[t._v("尾部补全")]),t._v("。")]),t._v(" "),s("div",{staticClass:"language-javascript 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number"}},[t._v("4")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'ab'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 'abax'")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'x'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("padEnd")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'ab'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 'xabab'")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'x'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("padEnd")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("4")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'ab'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 'xaba'")]),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，"),s("code",[t._v("padStart()")]),t._v("和"),s("code",[t._v("padEnd()")]),t._v("一共接受两个参数，第一个参数是字符串补全生效的最大长度，第二个参数是用来补全的字符串。")]),t._v(" "),s("p",[t._v("如果原字符串的长度，等于或大于最大长度，则字符串补全不生效，返回原字符串。")]),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 string"}},[t._v("'xxx'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("padStart")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'ab'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 'xxx'")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'xxx'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("padEnd")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'ab'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 'xxx'")]),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("如果用来补全的字符串与原字符串，两者的长度之和超过了最大长度，则会截去超出位数的补全字符串。")]),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 string"}},[t._v("'abc'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("padStart")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("10")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'0123456789'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// '0123456abc'")]),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("如果省略第二个参数，默认使用空格补全长度。")]),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 string"}},[t._v("'x'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("padStart")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("4")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// '   x'")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'x'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("padEnd")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("4")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 'x   '")]),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("code",[t._v("padStart()")]),t._v("的常见用途是为数值补全指定位数。下面代码生成 10 位的数值字符串。")]),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 string"}},[t._v("'1'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("padStart")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("10")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'0'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "0000000001"')]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'12'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("padStart")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("10")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'0'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "0000000012"')]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'123456'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("padStart")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("10")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'0'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "0000123456"')]),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("另一个用途是提示字符串格式。")]),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 string"}},[t._v("'12'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("padStart")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("10")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'YYYY-MM-DD'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "YYYY-MM-12"')]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'09-12'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("padStart")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("10")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'YYYY-MM-DD'")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// "YYYY-09-12"')]),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("h2",{attrs:{id:"实例方法-trimstart-修剪头部-trimend-修剪末尾"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#实例方法-trimstart-修剪头部-trimend-修剪末尾"}},[t._v("#")]),t._v(" 实例方法：trimStart() 修剪头部，trimEnd() 修剪末尾")]),t._v(" "),s("p",[s("a",{attrs:{href:"https://github.com/tc39/proposal-string-left-right-trim",target:"_blank",rel:"noopener noreferrer"}},[t._v("ES2019"),s("OutboundLink")],1),t._v(" 对字符串实例新增了"),s("code",[t._v("trimStart()")]),t._v("和"),s("code",[t._v("trimEnd()")]),t._v("这两个方法。它们的行为与"),s("code",[t._v("trim()")]),t._v("一致，"),s("code",[t._v("trimStart()")]),t._v("消除字符串头部的空格，"),s("code",[t._v("trimEnd()")]),t._v("消除尾部的空格。它们返回的都是新字符串，不会修改原始字符串。")]),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(" s "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token string"}},[t._v("'  abc  '")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\ns"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("trim")]),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('// "abc"')]),t._v("\ns"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("trimStart")]),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('// "abc  "')]),t._v("\ns"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("trimEnd")]),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('// "  abc"')]),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，"),s("code",[t._v("trimStart()")]),t._v("只消除头部的空格，保留尾部的空格。"),s("code",[t._v("trimEnd()")]),t._v("也是类似行为。")]),t._v(" "),s("p",[t._v("除了空格键，这两个方法对字符串头部（或尾部）的 tab 键、换行符等不可见的空白符号也有效。")]),t._v(" "),s("p",[t._v("浏览器还部署了额外的两个方法，"),s("code",[t._v("trimLeft()")]),t._v("是"),s("code",[t._v("trimStart()")]),t._v("的别名，"),s("code",[t._v("trimRight()")]),t._v("是"),s("code",[t._v("trimEnd()")]),t._v("的别名。")]),t._v(" "),s("h2",{attrs:{id:"实例方法-matchall"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#实例方法-matchall"}},[t._v("#")]),t._v(" 实例方法：matchAll()")]),t._v(" "),s("p",[s("code",[t._v("matchAll()")]),t._v("方法返回一个正则表达式在当前字符串的所有匹配，详见《正则的扩展》的一章。")])])}),[],!1,null,null,null);s.default=e.exports}}]);
    2.