Google Analytics javascript

Question

Here is a Google Analytics' code

var _gaq = _gaq || [];
_gaq.push(['_setAccount', 'UA-20366831-2']);
_gaq.push(['_trackPageview']);
(function () {
 var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
 ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
 var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
})();

How my client side calls Google anonymous function?

Answer 1

It's called because the anonymous function ends with ()

 var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
})(); // <--- The () calls the anonymous code

As you'll see, this code basically injects a script tag into the DOM, which gets run by the browser.

Answer 2

That snippet already call itself.

(function () {
 var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
 ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
 var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
})(); 

what it actually does is including the ga.js on your page, which is similar to this:

<script src="//google-analytics.com/ga.js" />

The rest is up to you to add event to the _gaq (google analytic queue). Then the event will automatically be processed.