Javascript Number zeropad(n)

Number.prototype.zeropad = function(n) {
   var str = "" + this;
   var len = n - str.length;
   var pad = "";
   while (len-- > 0) {
      pad += "0";
   }/*  w ww  .  j av  a 2s . c  o m*/
   return pad + str;
};