javascript - index.js 尝试导入错误 : './App' does not contain a default export (imported as 'App' )

Question

我正在尝试使用 React 构建我的第一个应用程序来显示 React bootstrap，但从 ./src/index.js 返回错误。

Attempted import error: './App' does not contain a default export (imported as 'App').

有人可以帮忙吗？

这是index.js:

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import * as serviceWorker from './serviceWorker';
import { Card } from "react-bootstrap";
import { Button } from "react-bootstrap";

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

const Example = (props) => {
    return (
        <Card style={ { width: "18rem" } }>
            <Card.Img variant="top" src="holder.js/100px180" />
            <Card.Body>
                <Card.Title>Card Title</Card.Title>
                <Card.Text>
                    Some quick example text to build on the card
                    title and make up the bulk of
                    the card's content.
                </Card.Text>
                <Button variant="primary">Go somewhere</Button>
            </Card.Body>
        </Card>
    );
};

export default Index;

serviceWorker.unregister();

import React from 'react';
import './App.css';
import "bootstrap/dist/css/bootstrap.min.css";
import { Card } from "react-bootstrap";
import { Button } from "react-bootstrap";

function App() {
    return (
        <Card style={ { width: "18rem" } }>
            <Card.Img variant="top" src="holder.js/100px180" />
            <Card.Body>
                <Card.Title>Card Title</Card.Title>
                <Card.Text>
                    Some quick example text to build on the card
                    title and make up the bulk of
                    the card 's content.
                </Card.Text>
                <Button variant="primary">Go somewhere</Button>
            </Card.Body>
        </Card>
    );
}

Answer 1

错误消息包含线索'./App'不包含默认导出(导入为'App')

解决方案是添加默认导出:

App.js

export default App;