Question

I’m looking at JQuery Tiny Pub/Sub, which looks something like this:

(function($){
  var o = $({});

  $.subscribe = function() {
    o.bind.apply( o, arguments );
  };

  ...

})(jQuery);

What I don’t get is, since the code is calling o.bind, the “this” inside bind is o anyway, therefore there is no reason to use apply.

In other words,

o.bind(arguments) 

and

o.bind.apply(o, arguments) 

here should be identical shouldn’t they? The why o.bind.apply(o, arguements)?

Answer 1

.apply takes an array of arguments to pass, so they’re not the same thing. Consider this:

function foo(a, b, c) {
    console.log(a);
    console.log(b);
    console.log(c);
}

foo.apply(null, [1, 2, 3]);
// Prints:
// 1
// 2
// 3

foo([1, 2, 3]);
// Prints:
// [1,2,3]
// undefined
// undefined

You may be confusing it with .call, which would certainly be redundant.