[removed] may fire multiple times

Question

Just because you don\'t see use for a feature doesn\'t mean it isn\'t useful.

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Answer 1

I think you could accomplish this with a timer (setInterval) that starts in the onbeforeunload callback. Javascript execution will be paused while the confirm dialog is up, then if the user cancels out the timed function could reset the alreadyPrompted variable back to false, and clear the interval.

Just an idea.

Ok I did a quick test based on your comment.

0
window.onbeforeunload = function () {
   setInterval(function () { $('#counter').html(++counter); }, 1);
   return "are you sure?";
}
window.onunload = function () { alert($('#counter').html()) };

In between the two callbacks #counter never got higher than 2 (ms). It seems like using these two callbacks in conjunction gives you what you need.

EDIT - answer to comment:

Close. This is what i was thinking

var promptBeforeLeaving = true,
    alreadPrompted = false,
    timeoutID = 0,
    reset = function () {
        alreadPrompted = false;
        timeoutID = 0;
    };

window.onbeforeunload = function () {
    if (promptBeforeLeaving && !alreadPrompted) {
        alreadPrompted = true;
        timeoutID = setTimeout(reset, 100);
        return "Changes have been made to this page.";
    }
};

window.onunload = function () {
    clearTimeout(timeoutID);
};