What are useful JavaScript methods that extends built-in objects? [closed]

Answer 1

I have used the Array.Map function outlined by Scott Koon a couple of times.

http://www.lazycoder.com/weblog/2009/08/12/a-simple-map-function-for-plain-javascript-arrays/

Array.prototype.map = function(fn) {
    var r = [];
    var l = this.length;
    for(i=0;i