how to kno which node a user belongs to when they login using firebase auth code example

Example 1: restrict the user from going to signup or login page if the user is already logged in firebase auth

var user = firebase.auth().currentUser;

if (user) {
  // User is signed in.
} else {
  // No user is signed in.
}

Example 2: firebase auth get current user

var user = firebase.auth().currentUser;var name, email, photoUrl, uid, emailVerified;if (user != null) {  name = user.displayName;  email = user.email;  photoUrl = user.photoURL;  emailVerified = user.emailVerified;  uid = user.uid;  // The user's ID, unique to the Firebase project. Do NOT use                   // this value to authenticate with your backend server, if                   // you have one. Use User.getToken() instead.}