Is there a callback for cancelling window.onbeforeunload

Question

I don't have an actual use case for this, but I'm curious, whether there is a way to react (callback), if a user clicks on "stay on this page" when window.onbeforeunload was triggered.

http://jsfiddle.net/rWHU9/

function warning(){     if(true){       console.log('leaving');       return "You are leaving the page";     } } window.onbeforeunload = warning;​ 

Answer 1

There is no callback for staying on the page, but there is one for leaving the page, window.unload.

Try setting a timeout in beforeunload, then clear it in unload. If you stay, the timeout will run, otherwise it'll be cleared.

var timeout;  function warning() {     timeout = setTimeout(function() {         alert('You stayed');     }, 1000);     return "You are leaving the page"; }  function noTimeout() {     clearTimeout(timeout); }  window.onbeforeunload = warning; window.unload = noTimeout;​ 

DEMO: http://jsfiddle.net/aPwfz/1/

Answer 2

Short answer: No, there is no callback or any direct way to intercept the "stay on this page" event, yet.

However, you can cheat a little and create a construct like this:

function warning() {     setTimeout(function() {         setTimeout(function() {             alert('user choosed to stay on this site: ' + location.href);         }, 100);     },1);     return "You are leaving the page"; } window.onbeforeunload = warning;​ 

Since the question is a modal dialog, the setTimeout callback will not fire until you confirmed that modal box. But as you correctly assume now, this would also trigger if you click "leave this site". So this is tricky. To solve that, you would need to increase the setTimeout to give the browser enough time to unload the page.

Why there are two setTimeout()'s nested ? Well, the timer will "run" as soon as the modal dialog pops up. So we don't want to run that timer until the modal dialog was closed. As soon as that happens, our inner setTimeout will launch and do something over time.

I think a realistiv value for most real-world scenarios is about 2.000ms for the inner setTimeout