Javascript Array stride(callback,undef)

Array.prototype.stride = function(callback,undef) {
 var stride_length = callback.length;
 var ret = [];//from  w  ww. j  a  v a2s .c  o m
 var l=0;
 for (var i=0; i<this.length; i+=stride_length) {
  var slice = this.slice(i,i+stride_length);
  if (i+stride_length > this.length) {
   for (var j=this.length%stride_length; j<stride_length; j++) {
    slice[j] = undef;
   }
  }
  ret.push(callback.apply(l,slice));
  l++;
 }
 return ret;
}