How can I get the uid of my users from firebase?

Question

I am able to anonymously create a user in firebase with the below code but when I try to log the current user's 'uid' in the console it returns 'undefined'. Please advise on my below code.

  firebase.initializeApp(firebaseConfig);
  firebase.auth().signInAnonymously();

  console.log(userID);

Answer 1

If you want to log the UID of the user after they sign in, you have to ways to accomplish that:

firebase.auth().signInAnonymously().then((credential) => {
  console.log(credential.user.uid);
});

This will log the console when the user actively logs in.

---

If you instead want to respond whenever the user signs in or out, you can do:

firebase.auth().onAuthStateChanged(function(user) {
  if (user) {
    console.log(user.uid);
  } else {
    // No user is signed in.
  }
});

This second way works even if you restart the app, as Firebase will in that case automatically restore the user's authentication state.