如何在web应用中使用Firebase实时数据库

<script src="https://www.gstatic.com/firebasejs/9.0.2/firebase-app.js"></script>
<script src="https://www.gstatic.com/firebasejs/9.0.2/firebase-database.js"></script>

const firebaseConfig = {
  apiKey: "YOUR_API_KEY",
  authDomain: "YOUR_AUTH_DOMAIN",
  databaseURL: "YOUR_DATABASE_URL",
  projectId: "YOUR_PROJECT_ID",
  storageBucket: "YOUR_STORAGE_BUCKET",
  messagingSenderId: "YOUR_MESSAGING_SENDER_ID",
  appId: "YOUR_APP_ID"
};

firebase.initializeApp(firebaseConfig);

const db = firebase.database();
db.ref("users/user1").set({
  name: "John",
  age: 25
});

const db = firebase.database();
db.ref("users/user1").once("value")
  .then((snapshot) => {
    const user = snapshot.val();
    console.log(user);
  });

const db = firebase.database();
db.ref("users/user1").on("value", (snapshot) => {
  const user = snapshot.val();
  console.log(user);
});