text: let cacheName = 'pwa_2021';
  let filesToCache = [
      'index.html',
      'css/style.css',
      'js/main.js'
  ];
  /* Start the service worker and cache all of the app's content */
  self.addEventListener('install', function(e) {
      e.waitUntil(
          caches.open(cacheName).then(function(cache) {
              return cache.addAll(filesToCache);
          })
      );
  });
  
  /* Serve cached content when offline */
  self.addEventListener('fetch', function(e) {
      e.respondWith(
          caches.match(e.request).then(function(response) {
              return response || fetch(e.request);
          })
      );
  });
  