Firebase authentication store data

firebase-auth.js

var messagesRef = new Firebase('https://brilliant-fire-3159.firebaseio.com/users');
var userId = 0;

// For user authentication
function authHandler(error, authData) {
  if (error) {
    console.log('Login Failed!', error);
  } else {
    // Set the gravatar
    document.getElementById('gravatar').src = authData.password.profileImageURL;
  }
}

// Log the user in with an email combination
messagesRef.authWithPassword({
  email    : '[email protected]',
  password : 'dean123'
}, authHandler);

messagesRef.onAuth(function(authData) {
   userId = authData.uid;
});

var messageField = document.getElementById('messageInput');
var messageResults = document.getElementById('results');

// Save data to firebase
function savedata(){
  var message = messageField.value;

  messagesRef.child('users').child(userId).push(
  {
  fieldName:'messageField', 
  text:message
  });
  messageField.value = '';
}

// Update results when data is added
messagesRef.child('users').child(userId).limitToLast(10).on('child_added', function (snapshot) {
    var data = snapshot.val();
  var message = data.text;

    if (message != undefined)
    {
      messageResults.value += '\n' + message;
    }
});