BeforeUnloadEvent

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.

Event BeforeUnloadEvent

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 Standard
# the-beforeunloadevent-interface

Browser compatibility

BCD tables only load in the browser

See also