SOURCE

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(prevState => ({
      isToggleOn: !prevState.isToggleOn
    }));
  }

  render() {
    return (
        <div>
            <h2>hello {this.props.name}</h2>
            <button onClick={this.handleClick}>
                {this.state.isToggleOn ? 'ON' : 'OFF'}
            </button>
            <button onClick={() => this.handleClick()}>
                {this.state.isToggleOn ? 'ON' : 'OFF'}
            </button>
        </div>
    );
  }
}

ReactDOM.render(
  <Toggle name="react" />,
  document.getElementById('root')
);

<div id="root"></div>