urbit/outside/commonmark/js/lib/from-code-point.js

// derived from https://github.com/mathiasbynens/String.fromCodePoint
/*! http://mths.be/fromcodepoint v0.2.1 by @mathias */
if (String.fromCodePoint) {

    module.exports = function (_) {
        try {
            return String.fromCodePoint(_);
        } catch (e) {
            if (e instanceof RangeError) {
                return String.fromCharCode(0xFFFD);
            }
            throw e;
        }
    }

} else {

  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
          ) {
              return String.fromCharCode(0xFFFD);
          }
          if (codePoint <= 0xFFFF) { // BMP code point
              codeUnits.push(codePoint);
          } else { // Astral code point; split in surrogate halves
              // http://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;
  };
  module.exports = fromCodePoint;
}