Why does my firebase onAuthStateChanged() trigger multiple times? (React Native)

Question

My firebase method onAuthStateChanged() trigger several times when I sign in and out using firebase-authentication according to console.log. Isn't it supposed to trigger only once at login and once at logout. The result is that when signing out, the navigation to a previous page is triggered several times. Here's the code:

componentDidMount() {
    fbAuth.onAuthStateChanged(user => this.loginFunc(user));
}

loginFunc(user) {
   if (user) {
     console.log('LOGGED IN');
}else {
  console.log('LOGGED OUT');
  this.props.navigation.navigate('FbLogin');
}
console.log('onAUTH LOGGED IN: ', user);
}

This is what the console looks like. As you can see both login and logout are triggered on just a single logout click. On login, it triggers twice....

LOGGED OUT
FbLogin.js:46 onAUTH:  null
LoggedIn.js:27 LOGGED OUT
LoggedIn.js:30 onAUTH LOGGED IN:  null
FbLogin.js:44 LOGGED OUT
FbLogin.js:46 onAUTH:  null

My logout button looks like this:

<TouchableHighlight //LOGOUT
   style={{
      ...
   }}
   onPress={() => {
      fbAuth.signOut();
      this.setState({ loginState: "You are logged out" });
   }}
   >
      <Text>Logout</Text>
   </TouchableHighlight>

Answer 1

Yes this is normal, onAuthStateChanged will keep triggering, I solved this by using this code:

  var authFlag = true;
  Firebase.onAuthStateChanged( user => {
    if(authFlag) {
      authFlag = false;
      if (user) {
        // Do something,
      }
      else {
        // Alert.alert("Auth Error")
      }
    }
  });