Passed in undefined argument in jQuery core source code

Question

I noticed that in the jQuery core, one of the two arguments passed in is undefined.

(function( window, undefined ) {

    // Use the correct document accordingly with window argument (sandbox)
    var document = window.document;
    var jQuery = (function() {
        // ...defintion of the rest of the core...
    window.jQuery = window.$ = jQuery;
})(window);

Can anyone explain why the second argument is undefined?

Thanks in advance!

Because undefined can be overwritten and this way it is guaranteed to be undefined... My opinion. — mhitza, Mar 22 '11 at 17:21
Because Resig wanted to see how many people he could get to ask about it on Stack Overflow. — Wayne, Mar 22 '11 at 18:02
possible duplicate of [jQuery question: what does it really mean?](http://stackoverflow.com/questions/5305634/jquery-question-what-does-it-really-mean) — hjpotter92, May 24 '13 at 11:58

score 2 · Answer 1 · answered Mar 22 '11 at 17:25

2

Undefined is a type but is also a global variable.

You can have a module that overwrites the value of undefined by doing undefined = whatever.

jQuery uses a immediate function to scope window and undefined.

https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/undefined

answered Mar 22 '11 at 17:25

masylum

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I marked rsp's as the answer, but this is also a good answer. Thanks masylum. – maximus Mar 28 '11 at 13:39

score 2 · Answer 2 · answered Mar 22 '11 at 17:31

2

Since someone could overwrite undefined like this

undefined = true;

Code of your immediate function will pass it as it should be (stay undefined). I think it's mentioned in 10 Things I Learned from the jQuery Source.

answered Mar 22 '11 at 17:31

yojimbo87

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Passed in undefined argument in jQuery core source code

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