我是Nodejs新手，正在研究Express js，現在我正在研究特定路由的“中間件函數”，我想知道“next有什麼用”，意味著在驗證“next”函數可以做什麼之後做 ？如果我們想移動/重定向到另一個函數那麼我們該怎麼做？什麼是“checkAuthentication”？這是我目前的程式碼
const express = require('express');
const app = express();
// Custom middleware function
const authMiddleware = (req, res, next) => {
// Check if user is authenticated
const isAuthenticated = checkAuthentication(req);
if (isAuthenticated) {
next();
} else {
// User is not authenticated, send an unauthorized response
res.status(401).send('Unauthorized');
}
};
// Middleware function is applied to specific routes
app.get('/protected', authMiddleware, (req, res) => {
res.send('Protected Route');
});
// Route handler
app.get('/', (req, res) => {
res.send('Home Page');
});
// Start the server
app.listen(3000, () => {
console.log('Server is listening on port 3000');
}); 
接下來是傳遞給中間件函數的回呼函數。您可以在不同的框架中找到它的不同名稱，但概念保持不變。
我將嘗試透過您的程式碼本身來解釋中間件。
const express = require('express'); const app = express(); function checkAuthentication(req) { /* I am considering this as my authentication function. When the user logged in, server has sent him a token, which now will act as a validator. */ if (req.headers.token) { const user = someFunctionToFetchUser(req.header.token) return user } else { return false } } /* Now I want a function to be there on each protected api routes to make user if user has a valid token then only allow them to interact with the data base otherwise throw an error */ const authMiddleware = (req, res, next) => { // Check if user is authenticated const isAuthenticated = checkAuthentication(req); if (isAuthenticated) { // Now you have verified the has valid a token. So allow user // to reach to the controller or any other middleware, if any. next(); } else { // User is not authenticated, send an unauthorized response res.status(401).send('Unauthorized'); } }; // Middleware function is applied to specific routes app.get('/protected', authMiddleware, (req, res) => { res.send('Protected Route'); }); // You can have any number of middlewares app.get('/protected', authMiddleware, someOtherMiddleware, (req, res) => { res.send('Protected Route'); }); // And also you can pass data from middleware to next middleware/controller also by attahching it with request function newMiddleware(req, res, next) { req.foo = "bar" //Now you can access this foo variable in next function. }