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What is middleware in Express.js?

Asked on Sep 21, 2025

Answer

Middleware in Express.js is a function that has access to the request and response objects and can modify them, end the request-response cycle, or call the next middleware function in the stack.

<!-- BEGIN COPY / PASTE -->
        const express = require('express');
        const app = express();

        // Simple middleware function
        function logger(req, res, next) {
            console.log(`Request Method: ${req.method}, Request URL: ${req.url}`);
            next(); // Pass control to the next middleware
        }

        // Use the middleware
        app.use(logger);

        app.get('/', (req, res) => {
            res.send('Hello, World!');
        });

        app.listen(3000, () => {
            console.log('Server is running on port 3000');
        });
        <!-- END COPY / PASTE -->

Additional Comment:

Middleware functions can perform a variety of tasks like logging, authentication, and error handling.
The "next" function is crucial as it passes control to the next middleware function.
Middleware can be applied globally with "app.use()" or to specific routes.
The order of middleware is important as it affects the flow of request handling.

✅ Answered with JavaScript best practices.

Ask any question about JavaScript here... and get an instant response.

What is middleware in Express.js?

Asked on Sep 21, 2025

Answer

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