callbacks-in-react-3.js

class MyChildComponent extends PureComponent {
  render() {
    this.props.callback('Hello World')
    console.log('Proof that I\'m always re-rendering')
    // return something to render
  }
}

class MyParentComponent extends Component {
  …

  render() {
    <MyChildComponent callback={ (fromChildArg) => { console.log(fromChildArg) } } />
  }
}