Example for loading new external data in response to updated props

updating-external-data-when-props-changes-using-promises.js

// This is an example of how to fetch external data in response to updated props,
// If you are using an async mechanism that does not support cancellation (e.g. a Promise).

class ExampleComponent extends React.Component {
  _currentId = null;

  state = {
    externalData: null
  };

  static getDerivedStateFromProps(nextProps, prevState) {
    // Store prevId in state so we can compare when props change.
    // Clear out previously-loaded data (so we don't render stale stuff).
    if (nextProps.id !== prevState.prevId) {
      return {
        externalData: null,
        prevId: nextProps.id
      };
    }

    // No state update necessary
    return null;
  }

  componentDidMount() {
    this._loadAsyncData(this.props.id);
  }

  componentDidUpdate(prevProps, prevState) {
    if (this.state.externalData === null) {
      this._loadAsyncData(this.props.id);
    }
  }

  componentWillUnmount() {
    // Prevent potential setState calls after unmount,
    // (Since these trigger DEV warnigs)
    _currentId = null;
  }

  render() {
    if (this.state.externalData === null) {
      // Render loading state ...
    } else {
      // Render real UI ...
    }
  }

  _loadAsyncData(id) {
    if (id === this._currentId) {
      // Data for this id is already loading
    }

    this._currentId = id;

    asyncLoadData(id).then(externalData => {
      // Only update state if the Promise that has just resolved,
      // Reflects the most recently requested external data.
      if (id === this._currentId) {
        this.setState({ externalData });
      }
    });
  }
}

@Stephen-ONeil I feel the same way, if (id === this._currentId) { is basically just an isMounted check ...

A bug:

componentDidUpdate(prevProps, prevState) {
    if (prevState.externalData === null) {
      this._loadAsyncData(this.props.id);
    }
  }

must read

componentDidUpdate(prevProps, prevState) {
    if (this.state.externalData === null) {
      this._loadAsyncData(this.props.id);
    }
  }

Yes, This will cause the second render to fail. Because prevState is having old data now.

Blog post have the correct code

Thanks for pointing out the typo. I often don't notice comments on Gists. I've updated the example.