Google Analytics Code Explanation

The code is minified. Using http://jsbeautifier.org/ you can revert that (sort off) and make it a bit more readable. Basically It's a small function that adds another javascript (www.google-analytics.com/analytics.js) to the dom using the same protocol, http or https.

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

First of all, I would pass this through a beautifier, e.g. http://jsbeautifier.org/

 (function (i, s, o, g, r, a, m) {
     i['GoogleAnalyticsObject'] = r;
     i[r] = i[r] || function () {
         (i[r].q = i[r].q || []).push(arguments)
     }, i[r].l = 1 * new Date();
     a = s.createElement(o),
     m = s.getElementsByTagName(o)[0];
     a.async = 1;
     a.src = g;
     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');

After that lets evaluate the closure 

(function (i, s, o, g, r, a, m) {
...
 })(window, document, 'script', '//www.google-analytics.com/analytics.js', 'ga');

by replacing each of the named parameters: i, s, o, g, r with their corresponding values window, document, 'script', '//www.google-analytics.com/analytics.js', 'ga'

Note that a and m parameters do not have input values and are more like result variables.

This would be roughly (not bothering about variable scope, etc.) equivalent to

(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');

In short what this code does in essence, is that it creates a new script tag with the line:

a = document.createElement('script'),

Then finds the first script tag

m = document.getElementsByTagName('script')[0];

Then it sets the newly created script tag to asynchronous execution (More insight on async execution could be obtained at Understanding Asynchronous Code in Layman's terms should you need it)

a.async = 1;

1 in the line above is equivalent to true, it is used 1 just because it is shorter.

After that the src of this script tag is set

 a.src = '//www.google-analytics.com/analytics.js';

Note that above no protocol (http or https) is specified in the URL. This would allow for the script to be loaded in the current browser protocol.

And finally it is inserted before the first script tag, so the browser could start loading it.

 m.parentNode.insertBefore(a, m)

So to summarize:

  1. We create a script tag
  2. We set it to load asynchronously async=true
  3. We insert this script tag, before the first script tag in the document

Specifics related to google analytics.

 window['ga'] = window['ga'] || function () {
     (window['ga'].q = window['ga'].q || []).push(arguments)
 }, window['ga'].l = 1 * new Date();

defines global function named ga that pushes its arguments in a queue Array (named q)

Then with the lines

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

it pushes these "events" in the queue Array.

When the script is loaded, it checks the value of GoogleAnalyticsObject, which earlier was set to point to the name of ga with the line

 window['GoogleAnalyticsObject'] = 'ga';

Hope this helps


Google has published the un-minified version of this code:

<!-- Google Analytics -->
<script>
/**
 * Creates a temporary global ga object and loads analytics.js.
 * Parameters o, a, and m are all used internally. They could have been
 * declared using 'var', instead they are declared as parameters to save
 * 4 bytes ('var ').
 *
 * @param {Window}        i The global context object.
 * @param {HTMLDocument}  s The DOM document object.
 * @param {string}        o Must be 'script'.
 * @param {string}        g Protocol relative URL of the analytics.js script.
 * @param {string}        r Global name of analytics object. Defaults to 'ga'.
 * @param {HTMLElement}   a Async script tag.
 * @param {HTMLElement}   m First script tag in document.
 */
(function(i, s, o, g, r, a, m){
  i['GoogleAnalyticsObject'] = r; // Acts as a pointer to support renaming.

  // Creates an initial ga() function.
  // The queued commands will be executed once analytics.js loads.
  i[r] = i[r] || function() {
    (i[r].q = i[r].q || []).push(arguments)
  },

  // Sets the time (as an integer) this tag was executed.
  // Used for timing hits.
  i[r].l = 1 * new Date();

  // Insert the script tag asynchronously.
  // Inserts above current tag to prevent blocking in addition to using the
  // async attribute.
  a = s.createElement(o),
  m = s.getElementsByTagName(o)[0];
  a.async = 1;
  a.src = g;
  m.parentNode.insertBefore(a, m)
})(window, document, 'script', '//www.google-analytics.com/analytics.js', 'ga');

// Creates a default tracker with automatic cookie domain configuration.
ga('create', 'UA-XXXXX-Y', 'auto');

// Sends a pageview hit from the tracker just created.
ga('send', 'pageview');
</script>
<!-- End Google Analytics -->

https://developers.google.com/analytics/devguides/collection/analyticsjs/tracking-snippet-reference

Zlatin's line by line explanation is still valid.


i['GoogleAnalyticsObject']=r; This is assigning 'ga' to the 'GoogleAnalyticsObject' property of 'window'

window['ga'] = window['ga'] || function(){
        (window['ga'].q = window['ga'].q || []).push(arguments)
    }, window['ga'].l = 1 * new Date();

This part is assigning the 'ga' property of window as a function (or itself if it already exists). The function then assigns the q property as an empty array and adds all of the functions arguments to it. It then assigns the l property the current timestamp (it's multiplied by 1 to force it as an integer).

The next lines just make a script tag and assign it some attributes such as source and async = true and then it adds this script tag to the document.

Tags:

Javascript

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