React-Pattern-AsyncLoadComponent.js

class A extends Component {
  constructor(props) {
    super(props);
    this.state = {
      B: undefined
    };
    import('./B').then(bModule => {
      this.setState({ B: bModule.default });
    });
  }
  render() {
    if (this.state.B) {
      return <this.state.B />;
    } else {
      return 'loading...';
    }
  }
}