text: importScripts('https://www.gstatic.com/firebasejs/3.9.0/firebase-app.js')
  importScripts('https://www.gstatic.com/firebasejs/3.9.0/firebase-messaging.js')
  firebase.initializeApp({
    'messagingSenderId': '858526725120'
  })
  
  const messaging = firebase.messaging()
  messaging.setBackgroundMessageHandler(function(payload) {
    console.log('[firebase-messaging-sw.js] Received background message ', payload)
    // Customize notification here
    const notificationTitle = 'Background Message Title'
    const notificationOptions = {
      body: 'Background Message body.',
      icon: '/apple-touch-icon.png'
    };
  
    return self.registration.showNotification(notificationTitle,
        notificationOptions)
  })
  