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 CheckBox extends React.Component{
    constructor(props){
      super(props);
      this.state = {checked: false};
    }

    changeState(){
      this.setState({
        checked : !this.state.checked
      });
    }

    render(){
      var msg;
      msg = this.state.checked ? 'Sim' : 'Não';
      return(
        <div>
          <input type="checkbox" defaultChecked={this.state.checked} onChange={this.changeState.bind(this)}/>
          <p>{msg}</p>
        </div>
      )
    }
  }

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