ES5 shim for binding functions is Javascript

Question

Below is a ES5 shim for JS binding.I dont understand self.apply in the bound function. I know how to use apply method, but where is self pointing to in this case ? It it supposed to be a
function, but here self looks like an object.

if ( !Function.prototype.bind ) {

       Function.prototype.bind = function( obj ) {

        var slice = [].slice,
        args = slice.call(arguments, 1),
        self = this,

        nop = function () {},

        bound = function () {
        return self.apply( this instanceof nop ? this : ( obj || {} ), // self in this line is supposed  
        to // represent a function ?
        args.concat( slice.call(arguments) ) );
        };

        nop.prototype = self.prototype;
        bound.prototype = new nop();
        return bound;
        };
  }

Answer 1

Have in mind that in javascript almost everything is an object.

So you have it right there:

self = this

So, self is not representing anything, self is the instance.

Answer 2

self is being used in the shim you have listed to accommodate the fact that this changes along with scope changes. Within the direct scope of the Function.prototype.bind function this will refer to the object on which the bind function was called.

Once you enter the scope of the nested bound function this has changed; so the author has assigned self = this within the bind function to allow the value of this at the time bind is called to remain available to the bound function via lexical scoping (closure).

Scoping within JavaScript can get pretty complicated; for a detailed explanation take a look at this article.

Everything you wanted to know about JavaScript scope.