ExtendableEvent: waitUntil() method
Note: This feature is only available in Service Workers.
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gives the service worker time to update database schemas and delete outdated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.
Syntax
waitUntil(promise)
Parameters
Return value
None (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
Specification |
---|
Service Workers # dom-extendableevent-waituntil |
Browser compatibility
BCD tables only load in the browser