String.fromCodePoint()

概要

静的なString.fromCodePoint() メソッドはコードポイントの指定されたシーケンスを使用することによって生成された文字列を返します。

構文

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

引数

num1, ..., numN

コードポイントのシーケンス

スロー

RangeError

無効なUnicodeコードポイントが引数で与えられたら(例 "RangeError: NaN is not a valid code point")、RangeErrorがスローされます。

説明

fromCodePoint()メソッドはStringの静的なメソッドなので、自ら生成したStringオブジェクトのメソッドとしてではなく、常に、String.fromCodePoint()として使用してください。

例

例: fromCodePoint()を使う

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

ポリフィル

String.fromCodePoint メソッドはECMAScript第６版に追加されました。まだすべてのWebブラウザや環境でサポートされていないかもしれません。互換性のために次のコードを使用してください。:

/*! 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;
    }
  }());
}

仕様

ブラウザ実装状況

関連情報

• String.fromCharCode()
• String.prototype.charAt()
• String.prototype.codePointAt()
• String.prototype.charCodeAt()