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Node.js

Express Middleware

Express middleware modifies requests before they reach the route.

Read Time

5 min read

Difficulty

Beginner

Last Updated

Jun 15, 2026

Version

v1.0.0

Introduction

Middleware functions sit in the middle, between the user's incoming request and the final route response. Developers use middleware to log visitors, check if a user is logged in, or format data before the main code runs.

Example

1/* this uses middleware */
2const myLogger = function (req, res, next) {
3  console.log('User visited the site');
4  next(); // Pass control to the next function
5}
6
7app.use(myLogger);

Key Points

Middleware functions run in order.
The `next()` function moves to the next middleware.
`app.use()` applies the middleware to all routes.
If you forget `next()`, the server gets stuck loading forever.

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