What is the point of undefined as function argument?

Asked Mar 06 '13 at 09:34

Active Mar 06 '13 at 09:45

Viewed 62 times

I keep seeing in OSS source code functions that have undefined as parameter, e.g. like this from fancybox:

(function (window, document, $, undefined) {
    "use strict";
    // snip-snip
}(window, document, jQuery));

;(function(defaults, $, undefined) {
   // snip, snip
})({
   // snip, snip settings
}, jQuery);

Is there some reason why?

EDIT: Okay, so I get it that it gets defined undefined locally but I have an issue with this, checking something is undefined won't work sometimes:

if (thing === undefined) {} 
    // will crash if thing has never been initialized

if (typeof thing === 'undefined') {} 
    // always works

Is there some performance gain to this or something?

edited Mar 06 '13 at 09:45

asked Mar 06 '13 at 09:34

Spoike

2

To avoid unexpected results when someone uses `var undefined=;` at the global level. – Rob W Mar 06 '13 at 09:35
1

Question already asked :) http://stackoverflow.com/questions/4650442/javascript-function-with-undefined-parameter – Alex Pereira Mar 06 '13 at 09:36
I tried to google it... failed. Which is why I asked this question in particular. – Spoike Mar 06 '13 at 09:37
so I edited the question a bit – Spoike Mar 06 '13 at 09:45
It's typically used to compare `obj.x` against `undefined` whereby `obj` is not null. – Ja͢ck Mar 06 '13 at 09:56

0 Answers0