Web/API/ExtendableEvent/waitUntil

The ExtendableEvent.waitUntil() method tells the event dispatcher that work is ongoing. It can also be used to detect whether that work was successful. In service workers, waitUntil() tells the browser that work is ongoing until the promise settles, and it shouldn't terminate the service worker if it wants that work to complete.

The install events in service workers use waitUntil() to hold the service worker in the installing phase until tasks complete. If the promise passed to waitUntil() rejects, the install is considered a failure, and the installing service worker is discarded. This is primarily used to ensure that a service worker is not considered installed until all of the core caches it depends on are successfully populated.

The activate events in service workers use waitUntil() to buffer functional events such as fetch and push until the promise passed to waitUntil() settles. This gives the service worker time to update database schemas and delete outdated caches, so other events can rely on a completely upgraded state.

The waitUntil() method must be initially called within the event callback, but after that it can be called multiple times, until all the promises passed to it settle.

Note: The behaviour described in the above paragraph was fixed in Firefox 43 (see bug 1180274).

Syntax

extendableEvent.waitUntil(promise);

Parameters

A Promise.

Example

Using waitUntil() within a service worker's install event:

addEventListener('install', event => {
  const preCache = async () => {
    const cache = await caches.open('static-v1');
    return cache.addAll([
      '/',
      '/about/',
      '/static/styles.css'
    ]);
  };
  event.waitUntil(preCache());
});

Specifications

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

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`waitUntil` Experimental'	Chrome Full support 40	Edge Full support 17	Firefox Full support 44	IE No support No	Opera Full support 24	Safari No support No	WebView Android Full support 40	Chrome Android Full support 40	Firefox Android Full support 44	Opera Android Full support 24	Safari iOS No support No	Samsung Internet Android Full support 4.0
Asynchronous `waitUntil` Experimental'	Chrome ?	Edge Full support 17	Firefox Full support 53	IE No support No	Opera ?	Safari No support No	WebView Android ?	Chrome Android ?	Firefox Android Full support 53	Opera Android ?	Safari iOS No support No	Samsung Internet Android ?

Legend

Full support: Full support
No support: No support
Compatibility unknown: Compatibility unknown
Experimental. Expect behavior to change in the future.': Experimental. Expect behavior to change in the future.