When A User Close The Browser Window How to control this action

I know that when a user leaves your website you can perform any action if you add some code to the onunload event like for example display an alert box, pop-up a window, etc. but when the user close the browser window instead which event is fired up??? how to control this action??? is it possible to add some code to perform when this happens????Best regards,

I think it should trigger the same event as it is fundamentally the same, body being unloaded. I have found this to be the case in Internet Explorer 7 and Firefox. There might be inconsistencies in other borwsers, though.