User exit detection

Is there a way to detect when the user leaves, like 'window.onExit' or something?

Why???

I just made this ping pong style game and I thought maybe it would work to call a cookie function and store the current score as the user left. Though of course when he leaves he is gone, just thought of it since calling such a function wouldnt take more than.. well not very long...

Anyway I found another way to do it

onUnLoad perhaps?