JavaScript function with 'undefined' parameter [duplicate]

Question

Going around Modernizr source code I have found strange thing:

window.Modernizr = (function(window,document,undefined) {

After that this function will be called with two arguments (this, this.document).

Why undefined is used here? Is it meaningful or it's just strange code-style?

Answer 1

Creates a local undefined in case someone redefines undefined somewhere in the scope chain.

Also provides a faster lookup since undefined is a global property, so the scope chain traversal is reduced.