sw.js

// Here comes the install event!
// This only happens once, when the browser sees this
// version of the ServiceWorker for the first time.
self.addEventListener('install', function (event) {
    // We pass a promise to event.waitUntil to signal how 
    // long install takes, and if it failed
    event.waitUntil(
      // We open a cache…
      caches.open('simple-sw-v1').then(function (cache) {
          // And add resources to it
          return cache.addAll([
            './',
            'index.html',
            'devfest_logo.png'
          ]);
      })
    );
});

// The fetch event happens for the page request with the
// ServiceWorker's scope, and any request made within that
// page
self.addEventListener('fetch', function (event) {
    // Calling event.respondWith means we're in charge
    // of providing the response. We pass in a promise
    // that resolves with a response object
    event.respondWith(
      // First we look for something in the caches that
      // matches the request
      caches.match(event.request).then(function (response) {
          // If we get something, we return it, otherwise
          // it's null, and we'll pass the request to
          // fetch, which will use the network.
          return response || fetch(event.request);
      })
    );
});