ReactJS:如果用户未登录，则重定向到登录页面

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

// 定义登录页面组件
const LoginPage = () => {
  // 登录逻辑代码
  // ...
  return <div>Login Page</div>;
};

// 定义其他页面组件
const HomePage = () => <div>Home Page</div>;
const ProfilePage = () => <div>Profile Page</div>;

// 定义私有路由组件，用于判断用户是否登录
const PrivateRoute = ({ component: Component, ...rest }) => {
  const isAuthenticated = false; // 根据实际情况判断用户是否登录
  return (
    <Route
      {...rest}
      render={(props) =>
        isAuthenticated ? (
          <Component {...props} />
        ) : (
          <Redirect to="/login" />
        )
      }
    />
  );
};

// 定义应用程序组件
const App = () => {
  return (
    <Router>
      <Route path="/login" component={LoginPage} />
      <PrivateRoute path="/home" component={HomePage} />
      <PrivateRoute path="/profile" component={ProfilePage} />
    </Router>
  );
};

export default App;