Does Google Analytics event tracking on links slow down the user experience?

Question

I am considering attaching onclick events to internal links on my site to do some Google Analytics event tracking. But I am concerned about performance. My understanding is that the workflow will change:

1. User clicks on hyperlink
2. A call is made to Google Analytics to send event tracking data
3. Browser waits for response from GA server
4. Browser follows the link and opens the new page.

I am concerned about the delay introduced by steps 2 and 3. So the questions are:

1. Is my understanding of the flow correct?
2. What's the typical delay (in milliseconds) that the call to GA event tracking introduces?

Answer 1

Event tracking works by making an image request from the Google servers. A problem is that following a link to a new URL stops any pending/in-progress requests.If the browser is opening a link to a new URL in the same window before the tracking request has been made, you can loose analytics data.

So step 3 isn't a wait, but a delay that has to be added in to allow the tracking image request to complete (or at least start). 100-150 milliseconds is long enough for the request, but short enough not to be noticed by users.

I use some variation of the following event tracking code (jQuery code):

$('.someClassForTracking').click(function(e){
  _gaq.push(['_trackEvent', category, action, ...]);
  if (this.target != '_blank') {
    e.preventDefault();
    var url = this.href;
    setTimeout(function(){location.href = url}, 150);
  }
});