为什么 Google 的分析跟踪代码首先执行？

Question

I was playing around with custom variables in Google Analytics and wasn't sure why the following actually works. Why does Google's tracking code get executed first, especially since it is at the bottom of the page?

Both scripts are in self-executing functions, so how does javascript determine which one to execute first?

 // top of the page
  <script type="text/javascript">
              $(function ()
              {
                    _gaq.push(['_setCustomVar', 1, 'Account', 'PartTime', 1]);
              });
        </script> 


// bottom of the page
        <script type="text/javascript">

            var _gaq = _gaq || [];
            _gaq.push(['_setAccount', 'UA-xxxxxxxxxx']);
            _gaq.push(['_setDomainName', '.xxxxxxxx.com']);
            _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);
            })();

         </script>  

Answer 1

The first one does execute first, and isn't in a self executing function.

It consists of a call to the $ function and has one argument: an anonymous function.

$ is a very badly named function. The name itself is meaningless and it has been adopted by half a dozen different libraries to do half a dozen different things.

In jQuery, if you pass a function to $ it runs that function when the ready event is triggered (but the end of the HTML document being parsed). This is probably what is happening here.