Why does jQuery pass the window object into their scope [duplicate]

Question

Ok so I'm writing myself a js library for a project and I have a question. Like most other libraries out there, to preserve my variable scope I am wrapping my code in this:

(function() {
// my code here
})();

Now my question is this: I notice jQuery passes in the window object and sets its own document object like this:

(function(window) {
var document = window.document;
})(window);

Does anyone know why they do this?

Answer 1

Yes! Since the window in this function is a local variable now it allows minify its name. Also access to the local variables should be faster than to the global ones.

Answer 2

You can access faster to local vars, also you can shorten the variable name "window" (and even "document") with something like:

(function(w, d)(){

    // use w and d var

})(window, document)