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String.fromCodePoint()是String的静态方法,该方法使用指定的unicode参数返回一个primitive的字符串。与fromCharCode功能类似,但是支持的Unicode字符更全,但是浏览器支持情况不是太好,目前ie以及safari还不支持。另外,性能并没有fromCharCode快。因为是ES6当中的新定义的特性,所以目前还不适合放到正式产品环境中去使用。
语法
String.fromCodePoint(num1[, ...[, numN]])
参数
num1, ..., numN
- 一串Unicode编码.
异常
RangeError
- 如果传入无效的Unicode编码,将会抛出一个
RangeError
(e.g. "RangeError: NaN is not a valid code point").
说明
因为 fromCodePoint()
是 String
的一个静态方法,所以只能通过String.fromCodePoint()这样的方式来使用,不能在字符串
String
对象的实例上直接调用。
例子
使用 fromCodePoint()
String.fromCodePoint(42); // "*" String.fromCodePoint(65, 90); // "AZ" String.fromCodePoint(0x404); // "\u0404" String.fromCodePoint(0x2F804); // "\uD87E\uDC04" String.fromCodePoint(194564); // "\uD87E\uDC04" String.fromCodePoint(0x1D306, 0x61, 0x1D307) // "\uD834\uDF06a\uD834\uDF07" String.fromCodePoint('_'); // RangeError String.fromCodePoint(Infinity); // RangeError String.fromCodePoint(-1); // RangeError String.fromCodePoint(3.14); // RangeError String.fromCodePoint(3e-2); // RangeError String.fromCodePoint(NaN); // RangeError
// String.fromCharCode() alone cannot get the character at such a high code point // The following, on the other hand, can return a 4-byte character as well as the // usual 2-byte ones (i.e., it can return a single character which actually has // a string length of 2 instead of 1!) console.log(String.fromCodePoint(0x2F804)); // or 194564 in decimal
Polyfill-浏览器补丁
String.fromCodePoint方法是ECMAScript2015(ES6)新增加的特性,所以一些老的浏览器可能还不支持。可以通过使用下面的polyfill代码来保证浏览器的支持:
/*! https://mths.be/fromcodepoint v0.1.0 by @mathias */ if (!String.fromCodePoint) { (function() { var defineProperty = (function() { // IE 8 only supports `Object.defineProperty` on DOM elements try { var object = {}; var $defineProperty = Object.defineProperty; var result = $defineProperty(object, object, object) && $defineProperty; } catch(error) {} return result; }()); var stringFromCharCode = String.fromCharCode; var floor = Math.floor; var fromCodePoint = function() { var MAX_SIZE = 0x4000; var codeUnits = []; var highSurrogate; var lowSurrogate; var index = -1; var length = arguments.length; if (!length) { return ''; } var result = ''; while (++index < length) { var codePoint = Number(arguments[index]); if ( !isFinite(codePoint) || // `NaN`, `+Infinity`, or `-Infinity` codePoint < 0 || // not a valid Unicode code point codePoint > 0x10FFFF || // not a valid Unicode code point floor(codePoint) != codePoint // not an integer ) { throw RangeError('Invalid code point: ' + codePoint); } if (codePoint <= 0xFFFF) { // BMP code point codeUnits.push(codePoint); } else { // Astral code point; split in surrogate halves // https://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae codePoint -= 0x10000; highSurrogate = (codePoint >> 10) + 0xD800; lowSurrogate = (codePoint % 0x400) + 0xDC00; codeUnits.push(highSurrogate, lowSurrogate); } if (index + 1 == length || codeUnits.length > MAX_SIZE) { result += stringFromCharCode.apply(null, codeUnits); codeUnits.length = 0; } } return result; }; if (defineProperty) { defineProperty(String, 'fromCodePoint', { 'value': fromCodePoint, 'configurable': true, 'writable': true }); } else { String.fromCodePoint = fromCodePoint; } }()); }
标准
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) String.fromCodePoint |
Standard | Initial definition. |
ECMAScript 2017 Draft (ECMA-262) String.fromCodePoint |
Draft |
浏览器兼容情况
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support |
41 |
29 (29) | 未实现 | 28 | 未实现 |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | 未实现 | 未实现 | 29.0 (29) | 未实现 | 未实现 | 未实现 |