How to determine Time On Site in Javascript?

Question

Google Analytics tracks 'Time On Site'. How would you do that effectively? Does it actually track when the user closes the browser or navigates away?

Thoughts?

Answer 1

I can't be 100% certain of course, but I would guess they use javascript and the onload and onunload events and/or setTimer to communicate with a web service via AJAX. This way they could figure out when users go to or leave a page on your site. Once the browser stops "pinging" the web service, it's assumed that they left your site.

I'm sure there's some margin of error involved no matter how you do it, but you could get a pretty decent estimate that way.

Answer 2

There is a javascript event called onBeforeUnload which executes when a user leaves a page. This could include closing the windows/tab or navigating to a different page(even if it's on the same site). By getting the time immediately after the page loads and using JavaScript to send a synchronous request onBeforeUnload with the difference in time between loading and leaving, you can effectively track the time spent on a page. I would assume this is what Google does.

If you want working code examples and a little more info, check this out.