Code for index.html when initializing Firebase for Flutter Web. Note: Use latest version of firebasejs. Link to video: https://youtu.be/l0cFOUJJcGQ

index.html

  <script src="https://www.gstatic.com/firebasejs/8.4.1/firebase-app.js"></script>
  <script src="https://www.gstatic.com/firebasejs/8.4.1/firebase-firestore.js"></script>
  <script src="https://www.gstatic.com/firebasejs/8.4.1/firebase-analytics.js"></script>

  <script>
  //Replace with your config data
  var firebaseConfig = {
    apiKey: "Anha1wShmI",
    authDomain: ".firebaseapp.com",
    projectId: "vacachal",
    storageBucket: "vac.appspot.com",
    messagingSenderId: "109037017",
    appId: "1:10903047017:web:9eb35c2756d9b878",
    measurementId: "G-M90GBQ2EKE"
  };
    
  // Initialize Firebase
  firebase.initializeApp(firebaseConfig);
  firebase.analytics();
  </script>