与props只能逐级传递数据相比，使用context可以实现跨级传递数据。
下面通过一个demo来展示context传递数据的实现：

//父组件，最上层的组件
import React,{ Component,PropTypes } from 'react';
import Son from './Son';

class App extends Component {

  getChildContext() {
      return {test: "hello"};
  }

  render() {
      return (
          <div className="App" style={{border:'1px solid red',width:'30%',margin:'50px auto',textAlign:'center'}}>
              <p style={{padding:'0',margin:'0'}}>父组件</p>
              <Son/>
          </div>
      );
  }
}

App.childContextTypes = {
    test: PropTypes.string
};

export default App;

//子组件
import React,PropTypes } from 'react';
import Grandson from './Grandson';

class App extends Component {
    render() {
        console.log('this.context',this.context);

        return (
            <div className="son" style={{border:'1px solid blue',width:'60%',textAlign:'center'}}>
                <p>子组件，获取父组件的值：{this.context.test}</p>
                <Grandson/>
            </div>
        );
    }
}
App.contextTypes = {
    test: PropTypes.string
};
export default App;

//孙组件
import React,PropTypes } from 'react';
class App extends Component {
    render() {
        console.log('this.context:',this.context);
        return (
            <div className="son" style={{border:'1px solid green',textAlign:'center'}}>
                <p>孙组件，获取传递下来的值：{this.context.test}</p>
            </div>
        );
    }
}
App.contextTypes = {
    test: PropTypes.string
};
export default App;

最终实现效果如下图