How to Fix Firebase Anonymous Auth Issues

In this tutorial, you'll learn about How to Fix Firebase Anonymous Auth Issues. We cover key concepts, practical examples, and best practices.

Firebase anonymous authentication fails — the user is not signed in after calling signInAnonymously(), or the anonymous account is lost when the page refreshes.

The Wrong Way

// Calling signInAnonymously on every page load
firebase.auth().signInAnonymously();

This creates a new anonymous account every time the page loads instead of restoring the existing session.

The Right Way

Step 1: Use onAuthStateChanged properly

firebase.auth().onAuthStateChanged((user) => {
  if (user) {
    // User is signed in (anonymous or permanent)
    return;
  }
  // No user — sign in anonymously
  firebase.auth().signInAnonymously()
    .catch(error => console.error('Anonymous sign-in failed:', error));
});

This preserves the anonymous session across page refreshes.

Step 2: Upgrade anonymous account to permanent

// When the user decides to create an account:
const credential = firebase.auth.EmailAuthProvider.credential(
  email, password
);

firebase.auth().currentUser.linkWithCredential(credential)
  .then((result) => {
    console.log('Anonymous account upgraded to:', result.user.email);
    // The previous anonymous UID is now the permanent account UID
    // All data associated with the anonymous UID is preserved
  });

Step 3: Check persistence setting

// Ensure persistence is set to local (default):
firebase.auth().setPersistence(firebase.auth.Auth.Persistence.LOCAL);
// LOCAL = survives page refresh
// SESSION = survives only within the current tab
// NONE = lost when page closes

Step 4: Handle anonymous sign-in errors

firebase.auth().signInAnonymously().catch(error => {
  if (error.code === 'auth/operation-not-allowed') {
    // Anonymous sign-in is not enabled in Firebase Console
    console.error('Enable anonymous auth in Firebase Console');
  }
});

Anonymous session persists — reload test: user stays signed in, data preserved, upgrade flow works.

Prevention

• Enable anonymous authentication in Firebase Console before deploying.
• Always call signInAnonymously() from onAuthStateChanged to avoid duplicate accounts.
• The anonymous-to-permanent upgrade flow is used by Doda Browser's guest mode — users can try the app before committing to an account.

Common Mistakes with auth anonymous

1. Placing the wildcard pattern first in case expressions, making all subsequent patterns unreachable
2. Using head and tail instead of pattern matching, causing runtime errors on empty lists
3. Forgetting that lazy evaluation defers computation until the value is forced, causing space leaks with unevaluated thunks

These mistakes appear frequently in real-world FIREBASE code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ

const provider = new firebase.auth.GoogleAuthProvider();
firebase.auth().currentUser.linkWithPopup(provider);