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

Answer 1

Function.prototype.bind from the Prototype library.

Similar to call and apply but allows you to return a reference to a function that is called in a particular context instead of executing it immediately. Also allows you to curry parameters. It's so useful that it became a part of ECMAScript 5 and is already being implemented natively in browsers.

Function.prototype.bind = function() {
  var __method = this, args = Array.prototype.slice.call(arguments), object = args.shift();
  return function() {
    var local_args = args.concat(Array.prototype.slice.call(arguments));
    if (this !== window) local_args.push(this);
    return __method.apply(object, local_args);
  }
}