Javascript Array indexOf(elem, from)

Array.prototype.indexOf = function(elem, from) {
 if (from == null) {
  from = 0;/*from  w ww .  j av  a  2s  .  c  o  m*/
 } else if (from < 0) {
  from = Math.max(0, this.length + from);
 }
 
 for (var i = from, len = this.length; i < len; i++) {
  if (this[i] === elem) {
   return i;
  }
 }
 
 return -1;
};