React Base Fiddle (JSX)

Starting point for creating JSFiddles with React.

HTML

<script src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>
<div id="container">
    <!-- This element's contents will be replaced with your component. -->
</div>

Babel + JSX

class AsyncState extends React.Component {
	state = {
		flag: false
  }
  async componentDidMount(){
  	const flag = await this.setFlagAsync();
    this.setState({flag})
  }
  
  async setFlagAsync(){
  	return new Promise((resolve, reject) => {
    	setTimeout(() => resolve(true), 2000)
    })
  }
  
  render() {
    return <div>
      {this.state.flag && <div>Done after 2 sec</div> || <div>Waiting for promise</div>}
    </div>;
  }
}

ReactDOM.render(
  <AsyncState />,
  document.getElementById('container')
);