How to ask confirmation when closing a window?

Question

I want to pop up a message asking for confirmation if the user wants to leave the current page, exactly like stackoverflow does it when you are typing a question.

Could someone help me on this, by giving me a script or redirecting me to an answer (on this site or elsewhere) ?

Thanks

Answer 1

You could use the onbeforeunload event.

window.onbeforeunload = function() {
   return 'Are you sure that you want to leave this page?';
};

Answer 2

You need to handle the window's onbeforeunload event and return a confirmation message as a string.

onunload will not work here. Demo