InstallEvent

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

The parameter passed into an install event handler function, the InstallEvent interface represents an install action that is dispatched on the ServiceWorkerGlobalScope of a ServiceWorker. As a child of ExtendableEvent, it ensures that functional events such as FetchEvent are not dispatched during installation.

This interface inherits from the ExtendableEvent interface.

Event ExtendableEvent InstallEvent

Constructor

InstallEvent()

Creates a new InstallEvent object.

Instance properties

Inherits properties from its parent, ExtendableEvent.

Instance methods

Inherits methods from its parent, ExtendableEvent.

addRoutes()

Specifies one or more static routes, which define rules for fetching specified resources that will be used even before service worker startup.

Examples

This code snippet is from the service worker prefetch sample (see prefetch running live.) The code calls ExtendableEvent.waitUntil() in ServiceWorkerGlobalScope.oninstall and delays treating the ServiceWorkerRegistration.installing worker as installed until the passed promise resolves successfully. The promise resolves when all resources have been fetched and cached, or when any exception occurs.

The code snippet also shows a best practice for versioning caches used by the service worker. Although this example has only one cache, you can use this approach for multiple caches. The code maps a shorthand identifier for a cache to a specific, versioned cache name.

Note: Logging statements are visible in Google Chrome via the "Inspect" interface for the relevant service worker accessed via chrome://serviceworker-internals.

js
const CACHE_VERSION = 1;
const CURRENT_CACHES = {
  prefetch: `prefetch-cache-v${CACHE_VERSION}`,
};

self.addEventListener("install", (event) => {
  const urlsToPrefetch = [
    "./static/pre_fetched.txt",
    "./static/pre_fetched.html",
    "https://www.chromium.org/_/rsrc/1302286216006/config/customLogo.gif",
  ];

  console.log(
    "Handling install event. Resources to pre-fetch:",
    urlsToPrefetch,
  );

  event.waitUntil(
    caches
      .open(CURRENT_CACHES["prefetch"])
      .then((cache) =>
        cache.addAll(
          urlsToPrefetch.map(
            (urlToPrefetch) => new Request(urlToPrefetch, { mode: "no-cors" }),
          ),
        ),
      )
      .then(() => {
        console.log("All resources have been fetched and cached.");
      })
      .catch((error) => {
        console.error("Pre-fetching failed:", error);
      }),
  );
});