BeforeUnloadEvent

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

See full compatibility

The BeforeUnloadEvent interface represents the event object for the beforeunload event, which is fired when the current window, contained document, and associated resources are about to be unloaded.

See the beforeunload event reference for detailed guidance on using this event.

Instance properties

Inherits properties from its parent, Event.

returnValue: When set to a truthy value, triggers a browser-controlled confirmation dialog asking users to confirm if they want to leave the page when they try to close or reload it. This is a legacy feature, and best practice is to trigger the dialog by invoking event.preventDefault(), while also setting returnValue to support legacy cases.

Instance methods

Inherits methods from its parent, Event.

Specifications

Specification
HTML # the-beforeunloadevent-interface

Browser compatibility

	desktop					mobile							server
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on iOS	Samsung Internet	WebView Android	WebView on iOS	Deno
`BeforeUnloadEvent`	Chrome – Full support Chrome 30 (Release date: 2013-10-01) footnote Full support	Edge – Full support Edge 12 (Release date: 2015-07-29) footnote Full support	Firefox – Full support Firefox 1.5 (Release date: 2005-11-29) footnote Full support	Opera – Full support Opera 17 (Release date: 2013-10-08) footnote Full support	Safari – Full support Safari 7 (Release date: 2013-10-22) footnote Full support	Chrome Android – Full support Chrome Android 30 (Release date: 2013-10-02) footnote Full support	Firefox for Android – Full support Firefox for Android 4 (Release date: 2011-03-29) footnote Full support	Opera Android – Full support Opera Android 18 (Release date: 2013-11-20) footnote Full support	Safari on iOS – Full support Safari on iOS 7 (Release date: 2013-09-18) footnote Full support	Samsung Internet – Full support Samsung Internet 3 (Release date: 2015-04-10) footnote Full support	WebView Android – Full support WebView Android 4.4 (Release date: 2013-12-09) footnote Full support	WebView on iOS – Full support WebView on iOS 7 (Release date: 2013-09-18) footnote Full support	Deno – Full support Deno 1.24 (Release date: 2022-07-20) footnote Full support
`returnValue` Deprecated	Chrome – Partial support Chrome 30 – 118 (Release date: 2013-10-01) footnote Partial support footnote Before Chrome 119, an empty string incorrectly activated the confirmation dialog. Chrome – Full support Chrome 119 (Release date: 2023-10-31) footnote Full support	Edge – Full support Edge 12 (Release date: 2015-07-29) footnote Full support	Firefox – Full support Firefox 1.5 (Release date: 2005-11-29) footnote Full support	Opera – Partial support Opera 17 – 104 (Release date: 2013-10-08) footnote Partial support footnote Before Opera 105, an empty string incorrectly activated the confirmation dialog. Opera – Full support Opera 105 (Release date: 2023-11-14) footnote Full support	Safari – Full support Safari 7 (Release date: 2013-10-22) footnote Full support	Chrome Android – Partial support Chrome Android 30 – 118 (Release date: 2013-10-02) footnote Partial support footnote Before Chrome Android 119, an empty string incorrectly activated the confirmation dialog. Chrome Android – Full support Chrome Android 119 (Release date: 2023-10-31) footnote Full support	Firefox for Android – Full support Firefox for Android 4 (Release date: 2011-03-29) footnote Full support	Opera Android – Partial support Opera Android 18 – 78 (Release date: 2013-11-20) footnote Partial support footnote Before Opera Android 79, an empty string incorrectly activated the confirmation dialog. Opera Android – Full support Opera Android 79 (Release date: 2023-12-06) footnote Full support	Safari on iOS – Full support Safari on iOS 7 (Release date: 2013-09-18) footnote Full support	Samsung Internet – Full support Samsung Internet 3 (Release date: 2015-04-10) footnote Full support	WebView Android – Partial support WebView Android 4.4 – 118 (Release date: 2013-12-09) footnote Partial support footnote Before WebView Android 119, an empty string incorrectly activated the confirmation dialog. WebView Android – Full support WebView Android 119 (Release date: 2023-10-31) footnote Full support	WebView on iOS – Full support WebView on iOS 7 (Release date: 2013-09-18) footnote Full support	Deno – No support Deno footnote No support
User interaction required for dialog box	Chrome – Full support Chrome 60 (Release date: 2017-07-25) footnote Full support	Edge – Full support Edge 79 (Release date: 2020-01-15) footnote Full support	Firefox – Full support Firefox 44 (Release date: 2016-01-26) footnote Full support	Opera – Full support Opera 47 (Release date: 2017-08-09) footnote Full support	Safari – Full support Safari 11 (Release date: 2017-09-19) footnote Full support	Chrome Android – Full support Chrome Android 60 (Release date: 2017-08-01) footnote Full support	Firefox for Android – Full support Firefox for Android 44 (Release date: 2016-01-26) footnote Full support	Opera Android – Full support Opera Android 44 (Release date: 2017-12-11) footnote Full support	Safari on iOS – Full support Safari on iOS 11 (Release date: 2017-09-19) footnote Full support	Samsung Internet – Full support Samsung Internet 8 (Release date: 2018-07-18) footnote Full support	WebView Android – Full support WebView Android 60 (Release date: 2017-08-01) footnote Full support	WebView on iOS – Full support WebView on iOS 11 (Release date: 2017-09-19) footnote Full support	Deno – No support Deno footnote No support

Tip: you can click/tap on a cell for more information.

Full support: Full support
Partial support: Partial support
No support: No support
: Deprecated. Not for use in new websites.
: Has more compatibility info.

BeforeUnloadEvent

Instance properties

Instance methods

Specifications

Browser compatibility

Legend

See also