Setup I’ve attached an event to the ‘window’ object, and I would like to

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Editorial Team

Asked: May 29, 20262026-05-29T18:09:08+00:00 2026-05-29T18:09:08+00:00

I’ve attached an event to the ‘window’ object, and I would like to check that it’s there via code.

window.addEventListener('beforeunload', function(e){ /*...*/ }, false)

I’ve tried the simple, and jQuery, without luck. I have more attempts up on jsFiddle.

window.beforeunload //is undefined as is window.onbeforeunload

$(window).data('events') //not working either

Is this possible?

There are similar questions (here and here) about the DOM, and other elements, but none of the approaches in those that I have tried have worked.

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Editorial Team · Answer 1 · 2026-05-29T18:09:09+00:00

Editorial Team

You can use the in operator…

'onbeforeunload' in window;  // true (if supported)

If supported, the property will exist, though the value will be null.

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