hello.js

/* @flow */
const React = require('react');
const ReactDOM = require('react-dom');

const {Component, PropTypes} = React;

type Props = typeof MyComponent.propTypes;
class MyComponent extends Component {
  props: Props;

  constructor(props:Props) {
    super(props);
  }

  render() {
    return (
      <div>{this.props.name}</div>
    );
  }
}
MyComponent.propTypes = {
  name: PropTypes.string.isRequired,
  hello: PropTypes.func,
};

ReactDOM.render(
  <MyComponent name={5} hello={() => 'world'} />,
  document.body
);

module.exports = MyComponent;