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.

Learning resources on MDN

• Window: beforeunload event

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 ❌ See webkit.org/b/219102

Baseline availability blocked since July 2015 by Safari on iOS (117 months)

View web-platform-tests results for this feature - View the feature source file (dist) - Edit the feature - Report an issue about this feature