How to set up AJAX call tracking in Google Analytics?

Question

I created my google analytics account. And copied and pasted the code provided into my index.php file. It seems to me that it works as I can see calls to www.google-analytics.com from firebug.

Now I want to track how many times the 'functions.php' is called via ajax from index file.

I tried to use _gaq.push(['_trackPageview', 'functions.php']); but it gave me Uncaught ReferenceError: _gaq is not defined. So I added var _gaq = _gaq || []; to my code. The error is gone but I cannot see any call to www.google-analytics.com after the ajax finishes.

Could someone help me to set it up so analytics would track ajax calls?

My code looks like

<script type='text/javascript'>
  (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-1234556-1', 'domain.com');
            ga('send', 'pageview');

         var _gaq = _gaq || [];

        function submit_data(){

                var text_area=$('#textarea').val();
                var url ="functions.php";
                jQuery.ajax({
                    type: "get",
                    dataType: "text",
                    url: url,
                    data: {
                        what : "generate",
                        text_area: text_area,
                        t: Math.random()
                    },
                        success: function(data, textStatus){
                        $('#textarea').val(data);
//                      _gaq.push(['_setAccount', 'UA-12345-1']);
                        _gaq.push(['_trackPageview', 'functions.php']);
                        }
                });
        }

        </script>

Answer 1

I think that at check in Google Analytics you select "Universal Analytics", and it uses a new code counter. Look in the browser DOM, there is no object "_gaq" - and is therefore an error. You tried to fix it with empty Array(_gaq).
Old code:

var _gaq = _gaq | | [];
_gaq.push (['_setAccount', 'UA-XXXXXX-1']);

Do not use old code! (And you can not use multiple codes counter 'UA-XXXXXX-1' - it's mistake)
New code:

ga ('create', 'UA-XXXXXXX-1', 'mysite.com');
ga ('send', 'pageview');

The new counter Google has a new syntax.
Documentation on the use of events: https://developers.google.com/analytics/devguides/collection/analyticsjs/events
Example of use:
I have a calculator on the page and I want to keep track of events by push of a button on it.
Category - "Using the Calculator";
Event - "Calculating the cost".
Old code:

_gaq.push(['_trackEvent', 'Using the Calculator', 'Calculating the cost');

New code:

ga('send', 'event', 'Using the Calculator', 'Calculating the cost');

Category and Event - is Required!
P.S.:Sorry. I have poor English and I used Google translator :)

Upd:

<script type='text/javascript'>

  (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');
//Use once per page
        ga('create', 'UA-1234556-1', 'domain.com');
        ga('send', 'pageview');
        //
        function submit_data(){

                var text_area=$('#textarea').val();
                var url ="functions.php";
                jQuery.ajax({
                    type: "get",
                    dataType: "text",
                    url: url,
                    data: {
                        what : "generate",
                        text_area: text_area,
                        t: Math.random()
                    },
                        success: function(data, textStatus){
                        $('#textarea').val(data);
                        ga('send', 'event', 'MyCategory', 'functions.php');
                        }
                });
        }

</script>

Answer 2

If you're using Universal Analytics (analytics.js) then switch this:

_gaq.push(['_trackPageview', 'functions.php']);

to this:

ga('send', 'pageview', 'functions.php');