Answers for "irebase app named '[default]' already exists with different options or config (app/duplicate-app)."

Firebase: Firebase App named '[DEFAULT]' already exists (app/duplicate-app).

if (!firebase.apps.length) {
    firebase.initializeApp({});
}

Firebase: Firebase App named '[DEFAULT]' already exists (app/duplicate-app).

if (!firebase.apps.length) {
    firebase.initializeApp(firebaseConfig);
}