class Toggle extends React.Component {
  constructor(props) {
    super(props);
    this.state = {isToggleOn: true};

    // This binding is necessary to make `this` work in the callback    this.handleClick = this.handleClick.bind(this);  }

  handleClick() {    this.setState(state => ({      isToggleOn: !state.isToggleOn    }));  }
  render() {
    return (
              {this.state.isToggleOn ? 'ON' : 'OFF'}
      
    );
  }
}

ReactDOM.render(
  ,
  document.getElementById('root')
);