text: import React, {Component} from 'react';
  import {Link} from 'react-router-dom';
  
  export default class Nav extends Component {
      render() {
          return (
              <ul>
                  <li><Link to="/">首页</Link></li>
                  <li><Link to="/page1">Page1</Link></li>
                  <li><Link to="/counter">Counter</Link></li>
                  <li><Link to="/userinfo">UserInfo</Link></li>
              </ul>
          )
      }
  }