Google Analytics Event Tracking and Variable visibility

I have added to my html page the standard latest snippet to get google analytics to work:

<script type="text/javascript"> 
  var _gaq = _gaq || []; 
  _gaq.push([开发者_运维问答'_setAccount', 'UA-15080849-1']); 
  _gaq.push(['_trackPageview']); 
  (function() { 
    var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; 
    ga.src = 'http://www.google-analytics.com/ga.js'; 
    (document.getElementsByTagName('head')[0] || document.getElementsByTagName('body')[0]).appendChild(ga); 
  })(); 
</script>
</body>
</html>

Now looking at the official 'event tracking guide' google says:

Add a snippet such as:

pageTracker._trackEvent('Videos', 'Play', 'Gone With the Wind');

where is pageTracker coming from? Is it a global object in ga.js? If it is, why does google not tell me that they run a risk of breaking some script?

You are using the async version of GA.

So your event tracking code should use that syntax. Instead of pageTracker._trackEvent('Videos', 'Play', 'Gone With the Wind');, you will want something like _gaq.push(['_trackEvent', 'Videos', 'Play', 'Gone With the Wind']);

Also, you can see more about the tracking method here (I can't post a second link yet):

code.google.com/apis/analytics/docs/gaJS/gaJSApiEventTracking.html

Does this help?

The migration guide for async analytics describes how to do event tracking asynchronously: http://code.google.com/apis/analytics/docs/tracking/asyncMigrationExamples.html#EventTracking

pageTracker is the global that most people use when using the traditional GA syntax. You don't need to use it for asynchronous GA. Instead you want:

_gaq.push(['_trackEvent', 'Videos', 'Play', 'Gone With the Wind']);