React-Router-Dom:不显示页面内容

import { BrowserRouter as Router, Route, Switch } from 'react-router-dom';
import Home from './Home';
import About from './About';

function App() {
  return (
    <Router>
      <Switch>
        <Route exact path="/" component={Home} />
        <Route path="/about" component={About} />
      </Switch>
    </Router>
  );
}

export default App;

// Home.js
import React from 'react';

function Home() {
  return <div>Home Page</div>;
}

export default Home;

npm install react-router-dom

import 'react-router-dom';

// App.js
import React from 'react';
import { BrowserRouter as Router, Route, Switch, Link } from 'react-router-dom';
import Home from './Home';
import About from './About';

function App() {
  return (
    <Router>
      <div>
        <nav>
          <ul>
            <li>
              <Link to="/">Home</Link>
            </li>
            <li>
              <Link to="/about">About</Link>
            </li>
          </ul>
        </nav>

        <Switch>
          <Route exact path="/" component={Home} />
          <Route path="/about" component={About} />
        </Switch>
      </div>
    </Router>
  );
}

export default App;

// Home.js
import React from 'react';

function Home() {
  return <div>Home Page</div>;
}

export default Home;

// About.js
import React from 'react';

function About() {
  return <div>About Page</div>;
}

export default About;