serviceworker.js

// Modified from https://gist.github.com/adactio/3717b7da007a9363ddf21f584aae34af
// All files: try the cache first, then the network. Cache a fresh version if possible.
// (beware: the cache will grow and grow; there's no cleanup)
const cacheName = 'files';

addEventListener('fetch', (fetchEvent) => {
  const request = fetchEvent.request;
  if (request.method !== 'GET') {
    return;
  }

  fetchEvent.respondWith(
    (async function () {
      const responseFromFetch = fetch(request);

      fetchEvent.waitUntil(
        (async function () {
          const responseCopy = (await responseFromFetch).clone();
          const myCache = await caches.open(cacheName);
          await myCache.put(request, responseCopy);
        })()
      );

      const responseFromCache = await caches.match(request);
      return responseFromCache || responseFromFetch;
    })()
  );
});