service-worker.js

// Fetch events, on registration of Service Worker...
self.addEventListener('fetch', (event) => {
    event.respondWith(caches.open('cache').then((cache) => {
      return cache.match(event.request).then((response) => {
        console.log("cache request: " + event.request.url);
         var fetchPromise = fetch(event.request).then((networkResponse) => {           
  // Update the cache...                   
  console.log("fetch completed: " + event.request.url, networkResponse);
    if (networkResponse) {
      console.debug("updated cached page: " + event.request.url, networkResponse);
        cache.put(event.request, networkResponse.clone());}
          return networkResponse;
            }, event => {   
  // Rejected promise - just ignore it, we're offline...  
            console.log("Error in fetch()", event);
            event.waitUntil(
  // Name the *cache* in the caches.open()...
            caches.open('cache').then((cache) => { 
            // Take a list of URLs, then fetch them from the server and add the response to the cache...
            return cache.addAll([                    
          './index.html', 
          './style/index.css', 
          './js/index.js', 
          './images/*'      
          ]);
        })
        );
      });
  // Respond from the cache, or the network...
    return response || fetchPromise;
  });
  }));
  });
  
  // Always updating i.e latest version available...
  self.addEventListener('install', (event) => {
      self.skipWaiting();
      console.log("Latest version installed!");
  });