DOM Window unload event, is it reliable?

Question

Can I rely on the window unload event to be triggered when a user closes a tab/window/browser?

Edit:

Found a list of what triggers the unload event in IE. http://msdn.microsoft.com/en-us/library/ms536973%28VS.85%29.aspx

I would like to know in which edge cases the unload event won't be triggered.

Answer 1

Not in all circumstances no. The browser could crash etc. keeping the event from firing. The user could also use add-ons like Grease Monkey to prevent the event from firing also.

Answer 2

You will likely want to use the "onbeforeunload" event too, it provides more control than the "onunload" event.

That said, be aware that: Opera doesn’t fire the unload event when the browser refreshes the page, or uses the back/forward buttons to browse off of the page. What’s worse, Opera never fires the onbeforeunload event. Thus if you are supporting Opera - be aware of these issues.