constructor() {
    super();
    this.ref = firebase.firestore().collection('posts');
    this.firestoreUnsubscriber = null;
    this.authUnsubscriber = null;
    this.state = {
      posts: [],
      loading: true,
      loggingIn: false,
      user: null,
      emailValue: '',
      passwordValue: '',
      hasError: false,
      error: '',
    };
  }

  componentDidMount() {
    this.authUnsubscriber = firebase.auth().onAuthStateChanged((user) => {
      this.setState({ user });
    });
    this.firestoreUnsubscriber = this.ref.onSnapshot(this.onCollectionUpdate)
  }

  componentWillUnmount() {
    if (this.authUnsubscriber) {
      this.authUnsubscriber();
    }
    if (this.firestoreUnsubscriber) {
      this.firestoreUnsubscriber();
    }
  }