ExtendableEvent.waitUntil

The ExtendableEvent.waitUntil() method extends the lifetime of the event. In service workers, extending the life of an event prevents the browser from terminating the service worker before asynchronous operations within the event have completed.

When called in an EventHandler associated to the install event, it delays treating the installing worker as installed until the passed Promise resolves successfully. This is primarily used to ensure that a service worker is not considered installed until all of the core caches it depends on are populated.

When called in an EventHandler associated to the activate event, it delays treating the active worker as activated until the passed Promise resolves successfully. This is primarily used to ensure that any functional events are not dispatched to the ServiceWorkerGlobalScope object until it upgrades database schemas and deletes the outdated Cache entries.

When the method runs, if the Promise is resolved, nothing happens. If the Promise is rejected, the state of the installing or active worker is set to redundant.

If waitUntil() is called outside of the ExtendableEvent handler, the browser should throw an InvalidStateError; note also that multiple calls will stack up, and the resulting promises will be added to the list of extend lifetime promises.

Syntax

event.waitUntil(promise)

Returns

None.

Parameters

A Promise.

Example

self.addEventListener('push', function(event) {
  console.log('Received a push message', event);

  var title = 'Yay a message.';
  var body = 'We have received a push message.';
  var icon = '/images/icon-192x192.png';
  var tag = 'simple-push-demo-notification-tag';

  event.waitUntil(
    self.registration.showNotification(title, {
      body: body,
      icon: icon,
      tag: tag
    })
  );
});

Specifications

Specification	Status	Comment
Service Workers The definition of 'waitUntil()' in that specification.	Working Draft	Initial definition

Browser compatibility

• [1] Before Chrome 46, waitUntil() would take any value rather than just promises.
• [2] Service workers (and Push) have been disabled in the Firefox 45 Extended Support Release (ESR.)

See also

• Using Service Workers
• Service workers basic code example
• Is ServiceWorker ready?
• Promise
• Using web workers