Binding onClick to this in react.js

binding_onClick.js

class Canvas extends Component {
  constructor(props) {
    super(props);

    var onClick;
    if (this.props.onClick) {
      onClick = this.props.onClick.bind(this);
    }

    this.state = {
      onClick: onClick,
    };
    this.doFoo = this.doFoo.bind(this);
  }

  render() {
    return (
      <div className="Canvas" onClick={ this.state.onClick }>
      </div>
    );
  }

  doFoo(bar) {}
}

function doFooOnClick() {
  this.doFoo(42);
}

ReactDOM.render(
  <Canvas onClick={ addWidgetOnClick }/>,
  document.getElementById('root');
);