jenot/priv/static/js/caching-worker.js

const putInCache = async (request, response) => {
  const cache = await caches.open("v1");
  await cache.put(request, response);
};

const cacheFirst = async ({ request, fallbackUrl }) => {
  const responseFromCache = await caches.match(request);
  if (responseFromCache) {
    return responseFromCache;
  }

  try {
    const responseFromNetwork = await fetch(request);
    // Cloning is needed because a response can only be consumed once.
    putInCache(request, responseFromNetwork.clone());
    return responseFromNetwork;
  } catch (error) {
    const fallbackResponse = await caches.match(fallbackUrl);
    if (fallbackResponse) {
      return fallbackResponse;
    }

    return new Response("Network error happened", {
      status: 408,
      headers: { "Content-Type": "text/plain" },
    });
  }
};

self.addEventListener("fetch", (event) => {
  const requestUrl = URL.parse(event.request.url);

  // We don't cache API requests
  if (!requestUrl.pathname.startsWith("/api")) {
    event.respondWith(
      cacheFirst({
        request: event.request,
        fallbackUrl: "/index.html",
      }),
    );
  }
});