Service Workers & Progressive Web Apps

self.addEventListener('fetch', event => {
  if (event.request.url.includes('large-file')) {
    event.respondWith(
      caches.open('large-files').then(cache => {
        return cache.match(event.request).then(response => {
          if (response) {
            fetch(event.request).then(freshResponse => {
              cache.put(event.request, freshResponse.clone());
            });
            return response;
          }
          return fetch(event.request);
        });
      })
    );
  }
});