content: import React from 'react';
  import ReactDOM from 'react-dom';
  /**
   * this.props.children代表当前组件使用的时候传入的子元素
   **/
  class Wrapper extends React.Component{
    render(){
       return (
         <div style={{border:'1px dashed red'}}>
           {this.props.children}
         </div>
       )
    }
  }
  
  ReactDOM.render(<Wrapper>
   <span>hello</span> <span>world</span>
  </Wrapper>,document.querySelector('#root'));