Javascript String rtrim(charlist)

String.prototype.rtrim = function (charlist) {
  charlist = !charlist ? ' \\s\u00A0' : (charlist + '').replace(/([\[\]\(\)\.\?\/\*\{\}\+\$\^\:])/g, '$1');
  var re = new RegExp('^[' + charlist + ']+', 'g');
  return this.replace(re, '');
};