text: importScripts('https://www.gstatic.com/firebasejs/3.6.8/firebase-app.js');
  importScripts('https://www.gstatic.com/firebasejs/3.6.8/firebase-messaging.js');
  
  firebase.initializeApp({
      messagingSenderId: '529760839731'
  });
  
  const messaging = firebase.messaging();
  