我使用以下命令安装了React.js:
create-react-app my-app
现在我打开命令行并执行以下命令:
npm start
应用程序在以下URL中在我的浏览器中打开:
http://localhost:3000/
现在我进入 public/src/app.js 文件夹并修改代码如下:
import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';
class App extends Component {
render() {
return (
<div className="App">
<header className="App-header">
<img src={logo} className="App-logo" alt="logo" />
<h1 className="App-title">Welcome to React</h1>
</header>
<p className="App-intro">
Why did you do ??
</p>
</div>
);
}
}
export default App;
以下内容如下:
import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';
ReactDOM.render(
<h1>Hello, world!</h1>,
document.getElementById('root')
);
export default App;
但我收到了以下错误。为什么?
Failed to compile
./src/App.js
Line 5: 'ReactDOM' is not defined no-undef
Line 10: 'App' is not defined no-undef
Search for the keywords to learn more about each error.