worker.js

// Names of the two caches used in this version of the service worker.
// Change to v2, etc. when you update any of the local resources, which will
// in turn trigger the install event again.
const PRECACHE = "precache-v1";
const RUNTIME = "runtime";

// A list of local resources we always want to be cached.
const PRECACHE_URLS = [
  "/", // Alias for index.html
];

// The install handler takes care of precaching the resources we always need.
self.addEventListener("install", (event) => {
  event.waitUntil(
    caches
      .open(PRECACHE)
      .then(function (cache) {
        console.log("Opened cache");
        return cache.addAll(PRECACHE_URLS);
      })
      .then(self.skipWaiting())
  );
});

// The activate handler takes care of cleaning up old caches.
self.addEventListener("activate", (event) => {
  const currentCaches = [PRECACHE, RUNTIME];
  event.waitUntil(
    caches
      .keys()
      .then((cacheNames) => {
        return cacheNames.filter(
          (cacheName) => !currentCaches.includes(cacheName)
        );
      })
      .then((cachesToDelete) => {
        return Promise.all(
          cachesToDelete.map((cacheToDelete) => {
            return caches.delete(cacheToDelete);
          })
        );
      })
      .then(() => self.clients.claim())
  );
});

// The fetch handler serves responses for same-origin resources from a cache.
// If no response is found, it populates the runtime cache with the response
// from the network before returning it to the page.
self.addEventListener("fetch", (event) => {
  // Skip cross-origin requests, like those for Google Analytics.
  if (event.request.url.startsWith(self.location.origin)) {
    event.respondWith(
      caches.match(event.request).then((cachedResponse) => {
        if (cachedResponse) {
          return cachedResponse;
        }

        return caches.open(RUNTIME).then((cache) => {
          return fetch(event.request).then((response) => {
            // Put a copy of the response in the runtime cache.
            return cache.put(event.request, response.clone()).then(() => {
              return response;
            });
          });
        });
      })
    );
  }
});