In IE and FF, i can attach an event handler to onBeforeUnload, and by passing a string to a property of the event, the user will see a dialog asking him whether he wants to continue with the "unloading" (either closing the window or navigating away).
Safari and Chrome don't support onBeforeUnload, and onUnload seems to be too late. Is there some way to replicate the same functionality in Safari/Chrome?
NOTE: I'm not trying to keep the user hostage. I know this is nagging and un-cool. In fact, my site goes to great lengths to let the user go freely, and have everything in its place when they come back. However, I am hosting other sites inside IFrames, and sometimes these decide to get rid of me and take over the browser, which is what I'm trying to avoid.
Thanks!
This works perfectly for me in both Chrome and Safari:
<html><body><p>Test</p>
<script>window.onbeforeunload = function() { return "Sure?"; }</script>
</body></html>
When I try to close the window, I get the prompt.
StackOverflow itself uses onbeforeunload, and it works fine for me in Safari:
function setConfirmUnload(a){window.onbeforeunload=a?function(){return a}:null}
I checked it in chrome and it seems to be working fine using this:
<body onunload="alert('x');" onbeforeunload="test1();">
This question is covered in slightly more detail in another newer StackOverFlow question: Setting onbeforeunload on body element in Chrome and IE using jQuery
来源：https://stackoverflow.com/questions/803887/can-i-pop-up-a-confirmation-dialog-when-the-user-is-closing-the-window-in-safari