[removed] may fire multiple times

Question

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

The Stack Exchange network, GMail, Grooveshark, Yahoo! Mail, and Hotmail use the onbe

Answer 1

I have encapsulated the answers from above in an easy to use function:

function registerUnload(msg, onunloadFunc) {
    var alreadPrompted = false,
        timeoutID = 0,
        reset = function() {
            alreadPrompted = false;
            timeoutID = 0;
        };

    if (msg || onunloadFunc) { // register
        window.onbeforeunload = function() {
            if (msg && !alreadPrompted) {
                alreadPrompted = true;
                timeoutID = setTimeout(reset, 100);
                return msg;
            }
        };

        window.onunload = function() {
            clearTimeout(timeoutID);
            if (onunloadFunc) onunloadFunc();
        };
    } else { // unregister
        window.onbeforeunload = null;
        window.onunload = null;
    }
}

To register use:

registerUnload("Leaving page", function() { /* unload work */ });

To unregister use:

registerUnload();

Hope this helps ..