text: // Must be located at the root.
  importScripts('https://cdn.jsdelivr.net/npm/firebase@6.6.2/firebase-app.js');
  importScripts('https://cdn.jsdelivr.net/npm/firebase@6.6.2/firebase-messaging.js');
  importScripts('firebase-init.js');
  
  firebase.initializeApp(FIREBASE_INIT);
  
  // This method shows the notifications.
  firebase.messaging().setBackgroundMessageHandler(function(payload) {
    let title = payload.data.title || "New message";
    let options = {
      body: payload.data.content || "",
      icon: '/img/logo96.png',
      badge: '/img/badge96.png',
      tag: payload.data.topic || undefined,
      data: {
        topic: payload.data.topic
      }
    };
    return self.registration.showNotification(title, options);
  });
  
  // Update service worker immediately for both the current client
  // and all other active clients.
  self.addEventListener('install', event => {
    self.skipWaiting();
  });
  
  // This code handles a click on notification: takes
  // the user to the browser tab with the chat or opens a new tab.
  self.addEventListener('notificationclick', event => {
    const notification = event.notification;
    notification.close();
  
    const urlHash = '#/' + notification.data.topic;
  
    event.waitUntil(self.clients.matchAll({
      type: 'window',
      includeUncontrolled: true
    }).then((windowClients) => {
      let anyClient = null;
      for (let i = 0; i < windowClients.length; i++) {
        const url = new URL(windowClients[i].url);
        if (url.hash.includes(notification.data.topic)) {
          // Found the Tinode tab with the right topic open.
          return windowClients[i].focus();
        } else {
          // This will be the least recently used tab.
          anyClient = windowClients[i];
        }
      }
  
      // Found tab with Tinode on a different topic,
      // navigate to the right topic.
      if (anyClient) {
        const url = new URL(anyClient.url);
        url.hash = urlHash;
        return anyClient.focus().then(thisClient => {
          return thisClient.navigate(url);
        });
      }
  
      // Did not find a Tinode browser tab. Open one.
      const url = new URL(self.location.origin);
      url.hash = urlHash;
      return clients.openWindow(url);
    }));
  });
  
  // This is needed for 'Add to Home Screen'.
  self.addEventListener('fetch', event => {
    // Workaround for https://bugs.chromium.org/p/chromium/issues/detail?id=823392
    if (event.request.cache == 'only-if-cached' && event.request.mode != 'same-origin') {
      return;
    }
    event.respondWith(
      //  Try to find response in cache.
      caches.match(event.request)
        .then((resp) => {
          // If response is found in cache, return it. Otherwise fetch.
          return resp || fetch(event.request);
        })
        .catch((err) => {
          // Something went wrong.
          console.log("Service worker Fetch: ", err);
        })
    );
  });
  