sw.js

self.addEventListener('fetch', function(event) {
  event.respondWith(caches.open('cache').then(function(cache) {
  return cache.match(event.request).then(function(response) {
  // console.log("cache request: " + event.request.url);
  var fetchPromise = fetch(event.request).then(function(networkResponse) {           
  // if we got a response from the cache, 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;
            }, function (event) {   
  // rejected promise - just ignore it, we're offline!   
            // console.log("Error in fetch()", event);
            event.waitUntil(
            caches.open('cache').then(function(cache) { 
  // our cache is named *cache* in the caches.open() above
            return cache.addAll
            ([            
  //cache.addAll(), takes a list of URLs, then fetches them from the server
  // and adds the response to the cache.           
  // add your entire site to the cache- as in the code below; for offline access
  // If you have some build process for your site, perhaps that could 
  // generate the list of possible URLs that a user might load.               
          '/', // do not remove this
          '/index.html', //default
          '/index.html?homescreen=1', //default
          '/?homescreen=1', //default
          '/assets/css/main.css',// configure as by your site ; just an example
          '/images/*',// choose images to keep offline; just an example
  // Do not replace/delete/edit the service-worker.js/ and manifest.js paths below
          '/service-worker.js',
          '/manifest.js',
  //These are links to the extenal social media buttons that should be cached;
  // we have used twitter's as an example
        // 'https://platform.twitter.com/widgets.js',       
          ]);
          })
          );
          });
  // respond from the cache, or the network
    return response || fetchPromise;
  });
  }));
  });
  
  self.addEventListener('install', function(event) {
    // The promise that skipWaiting() returns can be safely ignored.
    self.skipWaiting();
    console.log("Latest version installed!");
  });