404 page in REACT

All below example works fine:

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

Or if you want to return a simple 404 message without any component:

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

For those who are looking for an answer using react-router-dom v6, many things had changed. Switch for example doesn't exists anymore, you have to use element instead of component, ... Check this little example to get you an idea:

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')
)

With this you are defining your home route and all the other routes will show 404. Check the official guide for more info.

Try this one:

  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>

Try This:

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>