Is it possible to display a custom message in the beforeunload popup?

Question

When using window.onbeforeunload (or $(window).on(\"beforeonload\")), is it possible to display a custom message in that popup?

Maybe a sma

Answer 1

When using window.onbeforeunload (or $(window).on("beforeonload")), is it possible to display a custom message in that popup?

Not anymore. All major browsers have started ignoring the actual message and just showing their own.

By looking at existing answers I have the feeling this was possible in the past using things like confirm or alert or event.returnValue, but now it seems they are not working anymore.

Correct. A long time ago, you could use confirm or alert, more recently you could return a string from an onbeforeunload handler and that string would be displayed. Now, the content of the string is ignored and it's treated as a flag.

When using jQuery's on, you do indeed have to use returnValue on the original event:

$(window).on("beforeunload", function(e) {
    // Your message won't get displayed by modern browsers; the browser's built-in
    // one will be instead. But for older browsers, best to include an actual
    // message instead of just "x" or similar.
    return e.originalEvent.returnValue = "Your message here";
});

or the old-fasioned way:

window.onbeforeunload = function() {
    return "Your message here"; // Probably won't be shown, see note above
};

That's all you can do.