Why does Google Analytics dynamically inject javascript into the page

Question

Why do I need to use:

(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);
})();

Instead of:

<script async="true" type="text/javascript" src="http://www.google-analytics.com/ga.js"></script>

The only reason I can see is that they have a different subdomain for SSL. If it weren't for that is there any reason to use this script injection technique?

techfoobar · Accepted Answer · 2013-02-11 15:42:04Z

6

Being able to serve out http or https depending on the protocol of the parent page is one reason.
As the script is injected via a script tag inserted via running JS code, it does not block page loading. This is another reason. But this can very well be achieved via the new HTML5 async attribute too (but this is not compatible with older browsers - and GA absolutely needs to be compatible with pretty much all of them)

answered Feb 11, 2013 at 15:42

techfoobar

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8 Comments

T.J. Crowder Over a year ago

Primarily point #2 (and the subdomain). Point #1 could be solved by just starting the URL without a protocol (... src="//www.google-analytics.com/ga.js" ...).

techfoobar Over a year ago

@T.J.Crowder - Yes, that is also correct, but will it work for all browsers including older ones. Bcoz GA has to be super compatible with all i imagine.

marekful Over a year ago

Also, location.protocol can be used to dynamically detect the right protocol.

T.J. Crowder Over a year ago

@techfoobar: Compatible with anything you want to throw at it, see the link I added. :-)

techfoobar Over a year ago

@T.J.Crowder - Thank you for the informative article. So this in combo with async should mean no more script, maybe few more years down the line..

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