Thebackgroundfetchfail event of theServiceWorkerGlobalScope interface is fired when abackground fetch operation has failed: that is, when at least one network request in the fetch has failed to complete successfully.

This event is not cancelable and does not bubble.

Syntax

Use the event name in methods likeaddEventListener(), or set an event handler property.

addEventListener("backgroundfetchfail", (event) => { })onbackgroundfetchfail = (event) => { }

Event type

ABackgroundFetchUpdateUIEvent.

Event properties

Inherits properties from its parent,BackgroundFetchEvent.

BackgroundFetchUpdateUIEvent.updateUI()

Updates the UI of the element that the browser displays to show the progress of the fetch operation.

Description

When abackground fetch operation fails (meaning that at least one of the individual network requests has not completed successfully), the browser starts the service worker, if necessary, and fires thebackgroundfetchfail event in the service worker's global scope.

In the background fetch API, the browser shows a UI element to the user to indicate the progress of the operation. In thebackgroundfetchfail handler, the service worker can update that UI to show that the operation has failed. To do this, the handler calls the event'supdateUI() method, passing in a new title and/or icons.

In the handler for thisbackgroundfetchfail, the service worker can also clean up any related data for the operation. It can also retrieve and store any successful responses (for example, using theCache API). To access the response data, the service worker uses the event'sregistration property.

Examples

Updating UI

This event handler updates the UI to let the user know that the operation failed.

addEventListener("backgroundfetchfail", (event) => {  event.updateUI({ title: "Could not complete download" });});

Specifications

Browser compatibility

See also

• Background Fetch API