React路由组件未在页面上呈现

import { BrowserRouter as Router, Route } from 'react-router-dom';

function App() {
  return (
    <Router>
      <Route exact path="/" component={Home} />
      <Route path="/about" component={About} />
      {/* 其他路由规则 */}
    </Router>
  );
}

import { Route } from 'react-router-dom';

function App() {
  return (
    <div>
      <h1>My App</h1>
      <Route exact path="/" component={Home} />
      <Route path="/about" component={About} />
      {/* 其他路由规则 */}
    </div>
  );
}

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

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