reactjs - 在react.js中导出多个模块

Question

刚接触react.js并尝试关注tutorial 。不幸的是，页面中给出的代码不起作用。 webpack 提示

ERROR in ./App.jsx
Module build failed: SyntaxError: Only one default export allowed per module.

想知道如何修复它。谢谢。

=== App.jsx====

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><Link to = "/home">Home</Link></li>
               <li><Link to = "/about">About</Link></li>
               <li><Link to = "/contact">Contact</Link></li>
            </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;

=== main.js ===

import React from 'react';
import ReactDOM from 'react-dom';
import App from './App.jsx';

ReactDOM.render(<App/>, document.getElementById('app'));

更新1

我注释掉了所有导出默认值并在末尾添加了以下内容

module.exports = {
    App: App,
    Home: Home,
    About: About,
    Contact: Contact
}

现在没有编译错误，但网页是空白的。我不确定这里出了什么问题。

Answer 1

您只能有一个默认导出，您可以这样声明:

导出默认应用程序；或者导出默认类App extends React.Component {...

然后从'./App'导入App

如果您想导出更多内容，您可以使用 named 导出，您在声明时不使用 default 关键字，例如:

export {
  About,
  Contact,
}

或者:

export About;
export Contact;

或者:

export const About = class About extends React.Component {....
export const Contact = () => (<div> ... </div>);

然后你像这样导入它们:

import App, { About, Contact } from './App';

编辑:

教程中存在一个错误，因为无法在同一个 main.js 文件中进行 3 个默认导出。除此之外，如果没有在文件外部使用，为什么要导出任何内容呢？正确的 main.js :

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

class App extends React.Component {
...
}

class Home extends React.Component {
...
}


class About extends React.Component {
...
}


class Contact extends React.Component {
...
}


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'))

编辑2:

另一件事是，本教程基于react-router-V3，其API与v4不同。