What exactly does !function ($){...}(window.jQuery) do?

Question

I'd like to know exactly what's going on here. I know what $(document).ready(function() {...}); does and when it comes into effect. Same goes for jQuery(function($) {...}.

But what does this do?

!function ($) {
  $(function(){
    var $window = $(window)
    //normal jquery stuff
  })
}(window.jQuery)

Is it loaded when jQuery is loaded instead of when the document is 'ready'?

Answer 1

It creates a closure in which the variable $ is assigned the value of window.jQuery.

The intention is to allow the uninformatively named variable $ to be used as a shortcut for jQuery without conflicting with the large number of other libraries and custom functions that also use $ as a variable name.

Answer 2

Using the ! operator before the function causes it to be treated as an expression

!function () {}()