Javascript Array map(fun /*, thisp*/)

Array.prototype.map = function(fun /*, thisp*/) {
    var len = this.length;
    if (typeof fun != "function")
      throw new TypeError();//  ww w. j  ava  2 s  .c om

    var res = new Array(len);
    var thisp = arguments[1];
    for (var i = 0; i < len; i++)
    {
      if (i in this)
        res[i] = fun.call(thisp, this[i], i, this);
    }

    return res;
};