Javascript String padNum(amount)

String.prototype.padNum = function(amount) {
  var length = this.length;
  var newString = '';
  for (var i=0; i<amount-length; i++) {
    newString += '0';
  }/*from w  ww.  ja v  a 2  s .c  o  m*/
  newString += this;
  return newString;
}