“onbeforeunload” not firing on unload

Question

I stuck this in a.js file...

window.onbeforeunload = alert('onbeforeunload');

But it fires when the page is loaded, not when it is unloaded.
Does anyone know why?

Answer 1

change this:

window.onbeforeunload = alert('onbeforeunload');

to this

window.onbeforeunload = function () {alert('onbeforeunload');}

onbeforeunload takes a function reference which it will fire on before unload. You are technically assigning the return value of a function as the alert is firing when it is encountered on the page.

Answer 2

You have to wrap it... try this instead:

window.onbeforeunload = function(){alert('onbeforeunload')};