Firebase RTDB Component, before withDbData

rtdb-component.js

class Example extends React.Component {
  constructor(props) {
    super(props);
    this.state = { user: null, team: null };
  }
  componentDidMount() {
    let {userId, teamId} = this.props;
    // subscribe to user data
    let userRef = firebase.database().ref(`users/${userId}`);
    let userOff = userRef.on('value', (snap) => {
      this.setState({user: snap.val()});
    }
    this.userOff = () => ref.off('value', userOff);
    // subscribe to team data
    let teamRef = firebase.database().ref(`teams/${teamId}`);
    let teamOff = teamRef.on('value', (snap) => {
      this.setState({team: snap.val()});
    }
    this.teamOff = () => ref.off('value', teamOff);
  }
  componentDidUpdate(prevProps, prevState) {
    if (!prevState.user && this.state.user) {
        // first time we got user data!
    }
    if (!prevState.team && this.state.team) {
        // first time we got team data!
    }
  }
  componentWillUnmount() {
    this.userOff();
    this.teamOff();
  }
  render() {
    let { user, team } = this.state;
    if (!user || !team) {
      return null;
    }
    // ...
  }
}

export default Example