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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.

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 Deprecated: 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
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	WebView Android	WebView on iOS
`BeforeUnloadEvent`	30	12	1.5	17	7	30	4	18	7	3.0	4.4	7
`returnValue`	119 30–119 Before Chrome 119, an empty string incorrectly activated the confirmation dialog.	12	1.5	105 17–105 Before Opera 105, an empty string incorrectly activated the confirmation dialog.	7	119 30–119 Before Chrome Android 119, an empty string incorrectly activated the confirmation dialog.	4	79 18–79 Before Opera Android 79, an empty string incorrectly activated the confirmation dialog.	7	3.0	119 4.4–119 Before WebView Android 119, an empty string incorrectly activated the confirmation dialog.	7
`user_interaction`	60	79	44	47	11	60	44	44	11	8.0	60	11

BeforeUnloadEvent

Instance properties

Instance methods

Specifications

Browser compatibility

See also