// @flow
import React,{ Component } from 'react';

type Props<T> = {
  fetch: () => Promise<T>,
  cb: T => T,
};

class Client<T> extends Component<Props<T>> {

  componentDidMount() {
    const { fetch, cb } = this.props;
    fetch().then(cb);
  }

  render() {
    return (<div />)
  }
}

const App = <Client
              fetch={ () => Promise.resolve(1) }
              cb={ n => 'sfd' } />;