[рони]

Manyahin,

Array.prototype.each = function(fn) {
    for (var i=0; i<this.length; i++)  {this[i] = fn.call(this, this[i], i);}
    return this
}

alert([1,2,3].each(function (a)
{
   return a*a
}));

['test',false,12].each( function(el, i) {
  alert([el,i]);
  return el
})