logout time @ browser or tab closing

Hi,
I am doing some stuff in PHP.
When people log into my page ,i will show the logout button and so i can able to track the time of the logout.

But how to capture the time when they simple close the browser ?
Is it possible to do it php or js?
i need to know the time of the logout whether it is directly from browser or by browser close.

Any idea?

 

for this Please download the joomla and check how it's work. this is work on session with cookies.

 

Check with javascript "body onunload" event or Google it