service-worker.js

var version = 'app-v1';

var expectedCaches = [version];

self.oninstall = () => console.log('Installed version:', version);

self.onfetch = (event) => {
  event.respondWith(
    // Check cache for request
    caches.match(event.request)
    .then((cachedResponse) => {
      // If we have a cached response return it immediately unless this is an API request.
      // For those we'll only fallback to a cached response as a last resort
      if (cachedResponse &&
        cachedResponse.type !== 'error' &&
        !event.request.url.match('/api|jsonp')
      ) {
        console.log('Returning cached response ' + event.request.url, cachedResponse);
        return cachedResponse;
      }

      // Try to make the request
      return fetch(event.request.clone())
      .then((response) => {
        if (!response || response.status !== 200) {
          throw new Error('Invalid response ' + event.request.url);
        }

        return response.clone();
      })
      .then((response) => {
        const clonedRequest = event.request.clone();
        const clonedResponse = response.clone();

        // Cache the response
        caches.open(version).then((cache) => cache.put(clonedRequest, clonedResponse));

        // Return the live response
        console.log("Returning live response for", event.request.url);
        return response;
      }, (err) => {
        // Fallback to cached response if request fails
        return cachedResponse;
      });
    })
  );
};