Reactjs路由器:无法读取未定义(react-TypeError-toLowerCase)的属性“”react-router“”

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

import React from 'react';
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;

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

function Home() {
  return <h2>Home</h2>;
}

function About() {
  return <h2>About</h2>;
}

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

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

export default App;