Javascript Array last(predicate, def)

Array.prototype.last = function (predicate, def) {
 var l = this.length;
 if (!predicate) return l ? this[l - 1] : def == null ? null : def;
 while (l-- > 0){
  if (predicate(this[l], l, this))
   return this[l];
 }

 return def == null ? null : def;
};