How to show the “Are you sure you want to navigate away from this page?” when changes committed?

Question

Here in stackoverflow, if you started to make changes then you attempt to navigate away from the page, a javascript confirm button shows up and asks: \"Are you sure you want

Answer 1

The onbeforeunload Microsoft-ism is the closest thing we have to a standard solution, but be aware that browser support is uneven; e.g. for Opera it only works in version 12 and later (still in beta as of this writing).

Also, for maximum compatibility, you need to do more than simply return a string, as explained on the Mozilla Developer Network.

Example: Define the following two functions for enabling/disabling the navigation prompt (cf. the MDN example):

function enableBeforeUnload() {
    window.onbeforeunload = function (e) {
        return "Discard changes?";
    };
}
function disableBeforeUnload() {
    window.onbeforeunload = null;
}

Then define a form like this:

        
    Save

This way, the user will only be warned about navigating away if he has changed the text area, and will not be prompted when he's actually submitting the form.