import PropTypes from 'prop-types';
TodoItem.propTypes = {
    test: PropTypes.string.isRequired,   //加上isRequired以后，即使父组件没传递值也会抛出警告
}

var MyComponent = React.createClass({
  handleClick: function() {
    console.log(this.input)
  },
  render: function() {
    return (
      <div>
        <input type="text" ref={(input) => {this.input = input}} />
        <input type="button" value="Focus the text input" onClick={this.handleClick} />
      </div>
    );
  }
});

ReactDOM.render(
  <MyComponent />,
  document.getElementById('example')
);