ExtendableEvent: waitUntil() method
{{APIRef("Service Workers API")}} {{AvailableInWorkers("service")}}
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 {{domxref("ServiceWorkerGlobalScope/install_event", "install")}} events in service workers use
waitUntil() to hold the service worker in
the {{domxref("ServiceWorkerRegistration.installing", "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 {{domxref("ServiceWorkerGlobalScope/activate_event", "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gives the service worker time to update database schemas and delete outdated
{{domxref("Cache", "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.
Syntax
waitUntil(promise)
Parameters
promise- : A
{{jsxref("Promise")}}that extends the lifetime of the event.
- : A
Return value
None ({{jsxref("undefined")}} ).
Examples
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
{{Specifications}}
Browser compatibility
{{Compat}}