Why does jQuery file have two parameters in its function but receives only one parameter

Question

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

I am trying to learn about js scopes and anonymous functions. I have tried to read the jQuery.js file and it looks like this:

(function( window, undefined ) {

...

}(window));

Why does it have in the function params undefined when no parameter is being passed to it when it is executed?

It is already explained in here http://stackoverflow.com/questions/2716069/how-does-this-javascript-jquery-syntax-work-function-window-undefined — Andromeda, Sep 10 '12 at 07:54
Read ScottLahteine's comment in response to the top answer to [this question](http://stackoverflow.com/questions/776950/javascript-undefined-undefined). It's to ensure that, within the method, the variable called `undefined` is genuinely undefined. — Damien_The_Unbeliever, Sep 10 '12 at 07:56

score 9 · Accepted Answer · answered Sep 10 '12 at 07:54

This method is used so you can be sure that no one has previously redefined undefined value with something like

var undefined = true;

or with other tricky/evil assignments outside the jQuery scoped function. So, inside that function every comparison done against undefined is safe.

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