// service-worker.js

self.addEventListener('fetch', (event) => {
  // We have to duplicate a request
  // as it cannot be consumed twice.
  const duplicatedRequest = event.request.clone();

  event.respondWith(fetch(event.request).catch(err => {
    console.log(
      "Fetch failed. Trying to retrieve cache data.",
      err
    );

    return caches.match(duplicatedRequest);
  }));
});