Web features explorer - beforeunload

Web features explorer

The beforeunload event is fired when the current window is about to be unloaded. Typically this is used to display a dialog to confirm if users really want to leave the page when there is unsaved data that would be lost.

Browser support

Chrome 1 Released on 2008-12-11
Chrome Android 18 Released on 2012-06-27
Edge 12 Released on 2015-07-29
Firefox 1 Released on 2004-11-09
Firefox for Android 4 Released on 2011-03-29
Safari 3 Released on 2007-10-26
Safari on iOS Not supported Bugs: 219102

Baseline availability blocked since July 2015 by Safari (132 months)

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MDN documentation

Window: beforeunload event

Specifications

HTML (#the-beforeunloadevent-interface), from HTML Workstream (WHATWG).

Usage (according to Chrome Platform Status)

~57.123% of page loads. More data at chromestatus.com.

Web Platform Tests (WPT)

View the latest WPT test results for this feature

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