window.beforeunload called twice in Firefox - how to get around this?

Question

I'm creating a popup window that has a beforeunload handler installed. When the "Close" file menu item is used to close the popup, the beforeunload handler is called twice, resulting in two "Are you sure you want to close this window?" messages appearing.

This is a bug with Firefox, and I've reported it here, but I still would like a way to prevent this from happening. Can you think of a sane way of detecting double beforeunload to prevent the double message problem? The problem is that Firefox doesn't tell me which button in the dialog the user elected to click - OK or cancel.

Answer 1

Create a global variable that is set to true inside the handler. Only show the alert/popup when this variable is false.

Answer 2

Set a variable in the handler to prevent the dialog coming up the second time. Use setTimeout to reset it afterwards.

Answer 3

This is definitely a FF bug. I've reported it at https://bugzilla.mozilla.org/show_bug.cgi?id=531199

Answer 4

The best solution I've found is to use a flag global variable that is reset after so many milliseconds, say 500 (this ensures that the function can be called again, but not immediately after its appearance).

See last code in:

http://social.msdn.microsoft.com/Forums/en/sharepointinfopath/thread/13000cd8-5c50-4260-a0d2-bc404764966d

Answer 5

var onBeforeUnloadFired = false; window.onbeforeunload = function () { //if (window.clickHereDone == false) if (!onBeforeUnloadFired) { onBeforeUnloadFired = true; event.returnValue = "You have attempted to leave this page. If you have made any changes to the fields without clicking the Save button, your changes will be lost. Are you sure you want to exit this page?"; } window.setTimeout("ResetOnBeforeUnloadFired()", 10); } function ResetOnBeforeUnloadFired() { onBeforeUnloadFired = false; }