Javascript event onbeforeunload is not working properly in mozila firefox ... ?

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I am trying to show the confirmation popup while close the tab/browser of firefox but it is not working . I am using onbeforeunload event of javascript and using the following code :

window.onbeforeunload = DetectBrowserExit;

function DetectBrowserExit() {
return 'Are you sure to exit';
}

What I have tried:

window.onbeforeunload = DetectBrowserExit;

function DetectBrowserExit() {
return 'Are you sure to exit';
}

Posted 20-Sep-16 20:35pm

Adesh09

Updated 31-Jan-17 6:15am

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ZurdoDev 31-Jan-17 13:23pm

Put a breakpoint. Is it running the code?

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Sebastiaan Meijerink · Answer 1 · 2017-01-31T06:15:00

Solution 1

Please stop trying.

The onbeforeunload is a way to clean up localStorage or cookies.
Or maybe call a server script to delete session data.

But not the block the UI from closing you're page.

Most browsers will not allow you to do this and if they do, they stop doing it in the future.

It's considered harmfull

Posted 31-Jan-17 6:15am

Sebastiaan Meijerink

Comments

Richard Deeming 31-Jan-17 14:49pm

The onbeforeunload event is a perfectly valid and standard way of letting the user know that they're about to lose their work by navigating away from the page without saving.

Some browsers will allow the script to show a custom message; others display a standard message if any non-null value is returned from the event handler.

There is no suggestion that any major desktop browser is going to stop supporting this, and it is not considered harmful.

WindowEventHandlers.onbeforeunload | MDN[^]