CODEWITHSUNDEEP
javascriptgoogle-analytics
Mark
Mark

Reputation: 615

Loading js script like google analytics does and then run a function

I am trying to modify a js snippet that creates a js tag, it currently uses document.write which breaks the page removing all the existing DOM elements. I wanted to use something like google analytics does, my current code looks something like this:

var scr = document.createElement('script');
scr.type = 'text/javascript';
scr.async = true;
scr.src = ('https:' == document.location.protocol ? 'https://' : 'http://') + 'cdn.myurl.com/myscript.js';
var s = document.getElementsByTagName('script')[0];
s.parentNode.insertBefore(scr, s);

stuff.somefunc({
    userID: '2312312'
});

My problem is that stuff is obviously undefined, I want to avoid using some onload methods since I tried it in the past and had problems in some browsers. I tried to figure out how google analytics do it but my js skills are not that great. Here's the analytics sample:

(function (i, s, o, g, r, a, m) {
     window['GoogleAnalyticsObject'] = 'ga';
     window['ga'] = window['ga'] || function () {
         (window['ga'].q = window['ga'].q || []).push(arguments)
     }, window['ga'].l = 1 * new Date();
     a = document.createElement('script'),
     m = document.getElementsByTagName('script')[0];
     a.async = 1;
     a.src = '//www.google-analytics.com/analytics.js';
     m.parentNode.insertBefore(a, m)
 })(window, document, 'script', '//www.google-analytics.com/analytics.js', 'ga');

 ga('create', 'UA-xxxxxxxx-x', 'xxxxxx.com');
 ga('send', 'pageview');

How are they able to run ga()? As far as I can tell they are creating a global func with window['ga'] and pushing the arguments into an array to window['ga'].q, but what then? Is that window['ga'] function called inside analytics.js file? How?

Upvotes: 0

Views: 1746

Answers (1)

nyuen
nyuen

Reputation: 8907

ga() is executed because of the self-invoking anonymous function (SAIF) which does exactly that - it invokes or executes itself after being defined, with the arguments as provided in the parameters at the end.

This explains the GA code in detail: http://code.stephenmorley.org/javascript/understanding-the-google-analytics-tracking-code/

Upvotes: 2

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