Ajax problem in OnbeforeUnload in Chromium, Safari, and Opera

Question

1. AJAX call not works on onbeforeUnload event
2. alert box works properly on beforeunload

I want clear User login session when it click on back/refresh button or redirect by changes on URL in online system. I have implemented clear server side session using JavaScript for this by calling ajax onBeforeUnload event.

Instead of my expectation it not clearing a user session after redirecting a page. For testing purpose i have put alert box it displays as per my expectations BUT after closing alert box it redirects a page but not clear a server side session. It works fine in all other browsers as per my expectations.

Please help me for this..

Thanks