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

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 w开发者_Python百科ith 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.

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<script type="text/javascript">
var onBeforeUnloadFired = false;

window.onbeforeunload = function ()
{
    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;
}    
</script>

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

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

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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

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I've found this problem in Chrome 21, Firefox 14, IE 7-9, Safari 5 (on PC).

The following works on all of these browsers. If one removes the window.onbeforeunload function during the event this will prevent the second call. The trick is to reset the window.onbeforeunload function if the user decides to stay on the page.

var window_on_before_unload = function(e) {
    var msg;
    // Do here what you ever you need to do
    msg = "Message for user";

    // Prevent next "window.onbeforeunload" from re-running this code.
    // Ensure that if the user decides to stay on the page that
    // this code is run the next time the user tries to leave the page.
    window.onbeforeunload = set_on_before_unload;

    // Prepare message for user
    if (msg) {
        if (/irefox\/([4-9]|1\d+)/.test(navigator.userAgent))
            alert(msg
                    + '\n\nThe next dialog will allow you to stay here or continue\nSee Firefox bug #588292');

        (e = e || window.event).returnValue = msg;
        return msg;
    }
};

// Set window.onbeforeunload to the above handler.
// @uses window_on_before_unload
// @param {Event} e
var set_on_before_unload = function(e) {
    // Initialize the handler for window.onbeforeunload.
    window.onbeforeunload = window_on_before_unload;
}

// Initialize the handler for window.onbeforeunload.
set_on_before_unload();

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

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I use the following snippet to track the exitcount

When the page loads the following variable exitCount is initialized

if (typeof(MTG) == 'undefined') MTG = {};
MTG.exitCount=0; 

and in the Window unload event

$(window).bind("beforeunload", function(){


            if (MTG.exitCount<=0) 
            {

                             //do your thing, save etc
            }   
            MTG.exitCount++;




});

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I've found that instead of doing your own call to confirm(), just do even.preventDefault(); within the beforeunload event. Firefox throws up its own confirm dialog. I'm not sure if this is the correct/standard thing to do, but that's how they're doing it.

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I have a document opening another popup window with window.open. In the original window I have registered (with jquery) a listener for "unload" event like this:

var popup_window = window.open(...) 
$(popup_window).on('unload', function(event) ...

I have came across this page because the event was effectively triggering twice. What I have found is that it is not a bug, it triggers twice because it fires once for "about:blank" page being replaced by your page and another for your page being unloaded.

All I have to do is to filter the event that I am interested in by querying the original event:

function (event) {
   var original_url = e.originalEvent.originalTarget.URL;
   if (original_url != 'about:blank')
   {
       ... do cool things ...
   }
}

I don't know if this applies to the original question, because it is a special case of a window opening another, but I hope it helps.