Flutter Web和Firebase身份验证TypeError：无法读取未定义的属性'app'

Question

有人可以帮我吗？我尝试使用Flutter基于Google Firebase Auth和Cloud Firestore构建Web应用程序。 android上的项目运行良好，我可以与用户合作，并且可以从Cloud Firestore数据库中获取数据。我已经制作了第二个应用程序（webapp），执行Firebase文档中描述的所有步骤（webapp已注册，托管在Firebase上），并将所有依赖项插入pubspec.yaml

dependencies:
  flutter:
    sdk: flutter

  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for ios style icons.
  cupertino_icons: ^0.1.3
  firebase_core: ^0.4.4+3
  firebase: ^7.3.0
  firebase_auth: ^0.16.0

像这样修改index.html：

<body>
  <!-- The core Firebase JS SDK is always required and must be listed first -->
  <script src="/__/firebase/7.14.3/firebase-app.js"></script>

  <!-- TODO: Add SDKs for Firebase products that you want to use
     https://firebase.google.com/docs/web/setup#available-libraries -->
  <script src="/__/firebase/7.14.3/firebase-analytics.js"></script>
  <!-- Add Firebase products that you want to use -->
  <script src="https://www.gstatic.com/firebasejs/7.14.2/firebase-auth.js"></script>
  <script src="https://www.gstatic.com/firebasejs/7.14.2/firebase-firestore.js"></script>
  <!-- Initialize Firebase -->
  <script src="/__/firebase/init.js"></script>  <!-- This script installs service_worker.js to provide PWA functionality to
       application. For more information, see:
       https://developers.google.com/web/fundamentals/primers/service-workers -->
  <script>
    if ('serviceWorker' in navigator) {
      window.addEventListener('load', function () {
        navigator.serviceWorker.register('flutter_service_worker.js');
      });
    }
  </script>
  <script>
    var firebaseConfig = {
      apiKey: "XXXXXXXXXX-6EL5qIBxWjurRQMcK3pf9W-o",
      authDomain: "xxxxxxxx.firebaseapp.com",
      databaseURL: "https://xxxxxxxx.firebaseio.com",
      projectId: "xxxxxxxx",
      storageBucket: "xxxxxxxx.appspot.com",
      messagingSenderId: "xxxxxxxx6198",
      appId: "1:xxxxxxxx16198:web:cde3457e8dc734d045d227",
      measurementId: "X-XXXXXXXXXX"
    };
    firebase.initializeApp(firebaseConfig);
    firebase.auth();
    firebase.analytics();
  </script>
  <script src="main.dart.js" type="application/javascript"></script>
</body>

但是当我尝试登录或注册时，Android Studio会抛出此错误消息：

TypeError: Cannot read property 'app' of undefined
    at Object.app$ [as app] (http://localhost:53262/packages/firebase/src/top_level.dart.lib.js:72:56)
    at firebase_auth_web.FirebaseAuthWeb.new.[_getAuth] (http://localhost:53262/packages/firebase_auth_web/firebase_auth_web.dart.lib.js:42:27)
    at firebase_auth_web.FirebaseAuthWeb.new.signInWithCredential (http://localhost:53262/packages/firebase_auth_web/firebase_auth_web.dart.lib.js:197:34)
    at signInWithCredential.next (<anonymous>)
    at runBody (http://localhost:53262/dart_sdk.js:43135:34)
    at Object._async [as async] (http://localhost:53262/dart_sdk.js:43163:7)
    at firebase_auth_web.FirebaseAuthWeb.new.signInWithCredential (http://localhost:53262/packages/firebase_auth_web/firebase_auth_web.dart.lib.js:196:20)
    at firebase_auth.FirebaseAuth.__.signInWithCredential (http://localhost:53262/packages/firebase_auth/firebase_auth.dart.lib.js:324:90)
    at signInWithCredential.next (<anonymous>)

此异常是什么意思？我怎么了非常感谢您的帮助！