试试这个：

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

  <Switch>
    <Route path='/dashboard' component={Nav} />
    <Route path='/retrospectives' component={Nav} />
    <Route path='/users' component={Nav} />
    <Route path='/projects' component={Nav} />

    <Route path="" component={NotFound} />
  </Switch>

下面的例子都很好：

<Route path="" component={NotFound} /> // empty ""
<Route path="*" component={NotFound} /> // star *
<Route component={NotFound} /> // without path

或者如果你想返回一个简单的404消息，不带任何组件：

<Route component={() => (<div>404 Not found </div>)} />

对于那些正在使用react-router-dom v6寻找答案的人来说，很多事情已经改变了。例如Switch不再存在，你必须使用element而不是component，...检查这个小例子来让你有个想法：

import React from 'react'
import ReactDOM from 'react-dom'
import { BrowserRouter as Router, Routes, Route } from 'react-router-dom'

import './index.css'
import App from './App'

const Test = () => (
  <h1>404</h1>
)

ReactDOM.render(
  <React.StrictMode>
    <Router>
      <Routes>
        <Route path='/' element={<App />} />
        <Route path='*' element={<Test />}/>
      </Routes>
    </Router>
  </React.StrictMode>,
  document.getElementById('root')
)

这样你就定义了你的home路由，所有其他路由都将显示404。查看official guide以获取更多信息。

试试这个：

import React from "react";
import { Redirect, Route, Switch, BrowserRouter } from 'react-router-dom';
import HomePage from './pages/HomePage.jsx';
import NotFoundPage from './NotFoundPage.jsx';
class App extends React.Component {
    render(){
        return(
            <BrowserRouter>
                <Switch>
                    <Route exact path='/' component={HomePage} />
                    <Route path="*" component={NotFoundPage} />
                </Switch>
            </BrowserRouter>
        )
    }
}
   
export default App;

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>

只需从react-router-dom导入Switch，并将所有路由 Package 在交换机组件中。（就在你的switch结束标签之前）这样它会首先将每个组件与其路由进行匹配。如果匹配，它会渲染该组件，否则检查下一个。最终如果没有找到匹配的路由，它将呈现404Page

react router是一个让新手头疼的问题。使用这种代码格式。这是类组件，但你可以制作一个功能组件并使用它。

import React from "react";
import { BrowserRouter as Router, Routes, Route } from "react-router-dom";
import HomePage from './pages/HomePage.jsx';
import NotFoundPage from './NotFoundPage.jsx';
import Footer from './Footer';
class App extends React.Component {
    render(){
        return(
            <Router>
                <Routes>
                    <Route exact path='/' element={HomePage} />
                    <Route path="*" element={NotFoundPage} />
                </Routes>
                 <Routes>
                     <Route path="/" element={Footer}/>
                 </Routes>
            </Router>
        )
    }
}
   
export default App;

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

function App() {
  return (
    <>  
   <Router>
   <Routes>
   <Route exact path='/home' element={<Home/>}/>
    <Route exact path='/contact' element={<Contact/>}/>
    <Route exact path='/about' element={<About/>}/>
    <Route path="/404" element={<PageNotFound/>} />
    <Route path="*" element={<Navigate to="/404" />} />
   </Routes>
   </Router>
    </> 
  );
}
export default App;