Using JavaScript or jQuery how to check if event exists on the window?

Question

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.

user1106925 · Accepted Answer · 2012-02-14 01:39:48Z

10

You can use the in operator...

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

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

answered Feb 14, 2012 at 1:39

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3 Comments

Thanks. Works in IE, Chrome, but not FF.

@NickJosevski: Works for me in FF 10. When you say it doesn't work, what do you mean? What result are you getting?

Oh that's right, tested in FF 3.6... Works in 10. Thanks :) Problem still in Opera 11.61 but I can live with that.