Wittr app for Service Worker intro

index.js

self.addEventListener('install', function(event) {
  event.waitUntil(
    caches.open('wittr-static-v1').then(function(cache) {
      return cache.addAll([
        '/',
        'js/main.js',
        'css/main.css',
        'imgs/icon.png',
        'https://fonts.gstatic.com/s/roboto/v15/2UX7WLTfW3W8TclTUvlFyQ.woff',
        'https://fonts.gstatic.com/s/roboto/v15/d-6IYplOFocCacKzxwXSOD8E0i7KZn-EPnyo3HZu7kw.woff'
      ]);
    })
  );
});

     // TODO: respond with an entry from the cache if there is one.
    // If there isn't, fetch from the network.
self.addEventListener('fetch', function(event) {
	event.respondWith(caches.match(event.request)
		 .then(function(response) {
		 	if (response) return response;
		 	return fetch(event.request);
		 }));
});

indexController.js

import PostsView from './views/Posts';
import ToastsView from './views/Toasts';
import idb from 'idb';

export default function IndexController(container) {
  this._container = container;
  this._postsView = new PostsView(this._container);
  this._toastsView = new ToastsView(this._container);
  this._lostConnectionToast = null;
  this._openSocket();
  this._registerServiceWorker();
}

IndexController.prototype._registerServiceWorker = function() {
  if (!navigator.serviceWorker) return;

  navigator.serviceWorker.register('/sw.js').then(function() {
    console.log('Registration of Service Worker done!');
  }).catch(function() {
    console.log('Registration of Service Worker FAILED.');
  });
};

// open a connection to the server for live updates
IndexController.prototype._openSocket = function() {
  var indexController = this;
  var latestPostDate = this._postsView.getLatestPostDate();

  // create a url pointing to /updates with the ws protocol
  var socketUrl = new URL('/updates', window.location);
  socketUrl.protocol = 'ws';

  if (latestPostDate) {
    socketUrl.search = 'since=' + latestPostDate.valueOf();
  }

  // this is a little hack for the settings page's tests,
  // it isn't needed for Wittr
  socketUrl.search += '&' + location.search.slice(1);

  var ws = new WebSocket(socketUrl.href);

  // add listeners
  ws.addEventListener('open', function() {
    if (indexController._lostConnectionToast) {
      indexController._lostConnectionToast.hide();
    }
  });

  ws.addEventListener('message', function(event) {
    requestAnimationFrame(function() {
      indexController._onSocketMessage(event.data);
    });
  });

  ws.addEventListener('close', function() {
    // tell the user
    if (!indexController._lostConnectionToast) {
      indexController._lostConnectionToast = indexController._toastsView.show("Unable to connect. Retrying…");
    }

    // try and reconnect in 5 seconds
    setTimeout(function() {
      indexController._openSocket();
    }, 5000);
  });
};

// called when the web socket sends message data
IndexController.prototype._onSocketMessage = function(data) {
  var messages = JSON.parse(data);
  this._postsView.addPosts(messages);
};