class HelloWorldComponent extends React.Component {

  constructor(){

    super();

    this.state = {

      grade: 123

    }

  }

  handleInput(e) {

      //clear checkbox

    this.setState({

      grade: null

    })

  }

  render() {

    return (      

      <div>

      <div><input type="checkbox" onChange={this.handleInput.bind(this)}/></div>

      <div><input value={this.state.grade} type="number" name="3" /></div>

      </div>

    );

  }

}

​

React.render(

  <HelloWorldComponent name="Joe Schmoe"/>,

  document.getElementById('react_example')

);