Detecting Browser exit in PHP

Question

I have looked at a few topics (here & google) regarding detecting browser exit in php and im not really any clearer on how to do so.

I tried the register_s

Answer 1

PHP is a server side language. Browser events are handled by DOM events. On "onunload" or "onbeforeunload" events, sending an AJAX call to a PHP file.

And in this other question there is a flavored explanation of what I'm saying.