text: // Give the service worker access to Firebase Messaging.
  // Note that you can only use Firebase Messaging here, other Firebase libraries
  // are not available in the service worker.
  importScripts('https://www.gstatic.com/firebasejs/4.8.1/firebase-app.js');
  importScripts('https://www.gstatic.com/firebasejs/4.8.1/firebase-messaging.js');
  
  // Import and configure the Firebase SDK
  // These scripts are made available when the app is served or deployed on Firebase Hosting
  // If you do not serve/host your project using Firebase Hosting see https://firebase.google.com/docs/web/setup
  
  firebase.initializeApp({
      'messagingSenderId': '303951752448'
  });
  var messaging = firebase.messaging();
  
  /**
   * Here is is the code snippet to initialize Firebase Messaging in the Service
   * Worker when your app is not hosted on Firebase Hosting.
   // [START initialize_firebase_in_sw]
   // Give the service worker access to Firebase Messaging.
   // Note that you can only use Firebase Messaging here, other Firebase libraries
   // are not available in the service worker.
   importScripts('https://www.gstatic.com/firebasejs/4.8.1/firebase-app.js');
   importScripts('https://www.gstatic.com/firebasejs/4.8.1/firebase-messaging.js');
   // Initialize the Firebase app in the service worker by passing in the
   // messagingSenderId.
   firebase.initializeApp({
     'messagingSenderId': 'YOUR-SENDER-ID'
   });
   // Retrieve an instance of Firebase Messaging so that it can handle background
   // messages.
   const messaging = firebase.messaging();
   // [END initialize_firebase_in_sw]
   **/
  
  
  // If you would like to customize notifications that are received in the
  // background (Web app is closed or not in browser focus) then you should
  // implement this optional method.
  // [START background_handler]
  messaging.setBackgroundMessageHandler(function(payload) {
      console.log('[firebase-messaging-sw.js] Received background message ', payload);
      // Customize notification here
      var notificationTitle = payload.notification.title;
      var notificationOptions = {
          body: 'Background Message body.',
          icon: '/firebase-logo.png'
      };
  
      return self.registration.showNotification(notificationTitle,
          notificationOptions);
  });