我正在做这个路由器教程。

我的App.jsx文件：

import React from 'react';
import ReactDOM from 'react-dom';
import { Router, Route, Link, browserHistory, IndexRoute  } from 'react-router'

class App extends React.Component {
render() {
  return (
     <div>
        <ul>
           <li>Home</Link>
           <li>About</Link>
           <li>Contact</Link>
        </ul>

       {this.props.children}
     </div>
  )
 }
}

export default App;

class Home extends React.Component {
render() {
  return (
     <div>
        <h1>Home...</h1>
     </div>
  )
 }
}

export default Home;

class About extends React.Component {
render() {
  return (
     <div>
        <h1>About...</h1>
     </div>
  )
 }
}

export default About;

 class Contact extends React.Component {
render() {
  return (
     <div>
        <h1>Contact...</h1>
     </div>
  )
 }
}

export default Contact;

我的Main.js文件：

ReactDOM.render((
<Router history = {browserHistory}>
  <Route path = "/" component = {App}>
     <IndexRoute component = {Home} />
     <Route path = "home" component = {Home} />
     <Route path = "about" component = {About} />
     <Route path = "contact" component = {Contact} />
  </Route>
</Router>

), document.getElementById('app'))

该错误将写入控制台：index.js：

未捕获的ReferenceError：未定义ReactDOM

我真的不知道该怎么办。到目前为止，没有任何错误。在这里我不知道该怎么办。