class Toggle extends React.Component {

  constructor(props) {

    super(props);

    this.state = {isToggleOn: true};

​

    this.handleClick = this.handleClick.bind(this);

  }

​

  handleClick() {

    this.setState({

      isToggleOn: !this.state.isToggleOn

    });

  }

​

  render() {

    return (

      <button onClick={this.handleClick} className={this.state.isToggleOn}>

        {this.state.isToggleOn ? 'ON' : 'OFF'}

      </button>

    );

  }

}

​

ReactDOM.render(

  <Toggle />,

  document.getElementById('app')

);