Service worker exampe

sw.js

self.addEventListener('install', function(event) {
//   event.waitUntil(
//     caches.open('v1').then(function(cache) {
//       return cache.addAll([
//         '/sw-test/',
//         '/sw-test/index.html',
//         '/sw-test/style.css',
//         '/sw-test/app.js',
//         '/sw-test/image-list.js',
//         '/sw-test/star-wars-logo.jpg',
//         '/sw-test/gallery/bountyHunters.jpg',
//         '/sw-test/gallery/myLittleVader.jpg',
//         '/sw-test/gallery/snowTroopers.jpg'
//       ]);
//     })
//   );
});

self.addEventListener('fetch', function(event) {
  event.respondWith(caches.match(event.request).then(function(response) {
    // caches.match() always resolves
    // but in case of success response will have value
    if (response !== undefined) {
      return response;
    } else {
      return fetch(event.request).then(function (response) {
        // response may be used only once
        // we need to save clone to put one copy in cache
        // and serve second one
        let responseClone = response.clone();
        
//         caches.open('v1').then(function (cache) {
//           cache.put(event.request, responseClone);
//         });
        return response;
      }).catch(function (e) {
        console.log(e)
//         return caches.match('/sw-test/gallery/myLittleVader.jpg');
      });
    }
  }));
});