<HTML>
 <body>
     <div id="root"></div>
  
  
  <script crossorigin src="https://unpkg.com/react@16/umd/react.production.min.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@16/umd/react-dom.production.min.js"></script>

<!-- babel to transpile code to js. -->
 <script src="https://unpkg.com/babel-standalone@6.15.0/babel.min.js" ></script>
</body>
</HTML>
 class MainAppComponent extends React.Component {
    render() {
      return <h1>{this.props.greeting}</h1>
   }
 }
   
var App = <MainAppComponent greeting="Hello World !" />;
ReactDOM.render(App, document.getElementById('root'));
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