Question

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why do we need to pass in window and undefined into this jquery plugin?

I’ve seen jQuery source code does this:

(function(window, undefined){

...

}(window))

I get why is it useful to include undefined, if someone where to change “undefined” before. But window cant be changed. For all I know, it doesnt even need to be used, right? How could this be useful?

Answer 1

Micro optimisation.

Having window as a local variable is marginally faster than a global variable.

It also minifies better. We can now minify the function parameter to w and use w.setTimeout etc instead of window.setTimeout.

Fewer bytes = better