check if user is logged in firebase 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 update current user

var user = firebase.auth().currentUser;user.updateProfile({  displayName: "Jane Q. User",  photoURL: "https://example.com/jane-q-user/profile.jpg"}).then(function() {  // Update successful.}).catch(function(error) {  // An error happened.});