Question

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How does this JavaScript/JQuery Syntax work: (function( window, undefined ) { })(window)?

I am trying to breakdown some of the parts of jQuery to better understand what’s going on behind the scenes. For the most part, I am pretty clear on a lot of it’s methods, but the first line of code looks like this:

(function( window, undefined ) {

and the library ends like this

})( window );

I understand that this is immediate function invocation, but what does this do in context to the jQuery library? I’m not sure what I am looking at.

Also, where else would this be useful to us?

Answer 1

It is passing the current window object into jQuery so it has a reference to the window as a local object.

It is also not passing in a second parameter so that undefined will truly be “undefined”. The reason to do this is that it would be possible to assign undefined a value, so by expecting a value as a second parameter, but not getting one, jQuery is assuring itself that it really has undefined.