sw.js

/*
self.addEventListener('install', function(event) {
  event.waitUntil(
    caches.open('v1').then(function(cache) {
      return cache.addAll([
        '/pwademo/',
        '/pwademo/index.html',
        '/pwademo/style.css',
        '/pwademo/app.js',
        '/pwademo/image-list.js',
        '/pwademo/star-wars-logo.jpg',
        '/pwademo/gallery/bountyHunters.jpg',
        '/pwademo/gallery/myLittleVader.jpg'
      ]);
    })
  );
});
*/
self.addEventListener('fetch', function(event) {
  console.log(`---------------${event.request.url}`)
  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 () {
          return caches.match('/pwademo/gallery/myLittleVader.jpg');
        });
      }
    }));
});