JavaScript获得字符串实际长度

String.prototype.getRealLen = function() {
  var realLength = 0, len = this.length, charCode = -1;
  for (var i = 0; i < len; i++) {
    charCode = this.charCodeAt(i);
    if (charCode >= 0 && charCode <= 128) realLength += 1;
    else realLength += 2;
  }
  return realLength;
};