String.fromCodePoint() 静态方法返回使用指定的代码点序列创建的字符串。

语法

String.fromCodePoint(num1[, ...[, numN]])

参数

num1, ..., numN
一串 Unicode 编码位置,即“代码点”。

返回值

使用指定的 Unicode 编码位置创建的字符串。

异常

RangeError
如果传入无效的 Unicode 编码,将会抛出一个RangeError (例如: "RangeError: NaN is not a valid code point")。

说明

该方法返回一个字符串,而不是一个 String 对象。

因为 fromCodePoint()String 的一个静态方法,所以只能通过 String.fromCodePoint() 这样的方式来使用,不能在你创建的 String 对象实例上直接调用。

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() 方法不能单独获取在高代码点位上的字符
// 另一方面,下列的示例中,可以返回 4 字节,也可以返回 2 字节的字符
// (也就是说,它可以返回单独的字符,使用长度 2 代替 1!) 
console.log(String.fromCodePoint(0x2F804)); // or 194564 in decimal

Polyfill

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:

if (!String.fromCodePoint) (function(stringFromCharCode) {
    var fromCodePoint = function(_) {
      var codeUnits = [], codeLen = 0, result = "";
      for (var index=0, len = arguments.length; index !== len; ++index) {
        var codePoint = +arguments[index];
        // correctly handles all cases including `NaN`, `-Infinity`, `+Infinity`
        // The surrounding `!(...)` is required to correctly handle `NaN` cases
        // The (codePoint>>>0) === codePoint clause handles decimals and negatives
        if (!(codePoint < 0x10FFFF && (codePoint>>>0) === codePoint))
          throw RangeError("Invalid code point: " + codePoint);
        if (codePoint <= 0xFFFF) { // BMP code point
          codeLen = codeUnits.push(codePoint);
        } else { // Astral code point; split in surrogate halves
          // https://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
          codePoint -= 0x10000;
          codeLen = codeUnits.push(
            (codePoint >> 10) + 0xD800,  // highSurrogate
            (codePoint % 0x400) + 0xDC00 // lowSurrogate
          );
        }
        if (codeLen >= 0x3fff) {
          result += stringFromCharCode.apply(null, codeUnits);
          codeUnits.length = 0;
        }
      }
      return result + stringFromCharCode.apply(null, codeUnits);
    };
    try { // IE 8 only supports `Object.defineProperty` on DOM elements
      Object.defineProperty(String, "fromCodePoint", {
        "value": fromCodePoint, "configurable": true, "writable": true
      });
    } catch(e) {
      String.fromCodePoint = fromCodePoint;
    }
}(String.fromCharCode));

规范

规范 状态 备注
ECMAScript 2015 (6th Edition, ECMA-262)
String.fromCodePoint
Standard Initial definition.
ECMAScript Latest Draft (ECMA-262)
String.fromCodePoint
Draft  

浏览器兼容性

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
fromCodePointChrome Full support 41Edge Full support 12Firefox Full support 29IE No support NoOpera Full support 28Safari Full support 10WebView Android Full support YesChrome Android Full support YesFirefox Android Full support 29Opera Android Full support YesSafari iOS Full support 10Samsung Internet Android Full support Yesnodejs Full support 4.0.0
Full support 4.0.0
Full support 0.12
Disabled
Disabled From version 0.12: this feature is behind the --harmony runtime flag.

Legend

Full support  
Full support
No support  
No support
User must explicitly enable this feature.
User must explicitly enable this feature.

参见

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