Express Router: Grouping and Mounting Explained

Express Router: Grouping and Mounting Explained

express.Router is a mini-app you can mount under a path. It is how you keep your Express code organized as it grows.

Why Use express.Router

Putting every route in app.js works for tiny apps. As features grow, app.js becomes a mess. express.Router lets you split routes by feature (auth, users, feed, chat) into separate files.

Creating a Router

// routes/users.js
const express = require('express');
const router = express.Router();

router.get('/', listUsers);
router.post('/', createUser);
router.get('/:id', getUser);
router.patch('/:id', updateUser);
router.delete('/:id', deleteUser);

module.exports = router;

Mounting the Router

// app.js
app.use('/users', require('./routes/users'));

Now /users hits router.get('/', ...), /users/:id hits router.get('/:id', ...), and so on. The router's paths are relative to the mount path.

Per-Router Middlewares

You can apply middlewares to all routes in a router:

// routes/admin.js
const router = express.Router();
router.use(authenticate);
router.use(requireAdmin);
router.get('/stats', getStats);

Every route in admin.js now requires auth and admin. No need to repeat per route.

Nested Routers

Routers can be mounted inside routers:

// routes/users.js
const postsRouter = require('./posts');
router.use('/:userId/posts', postsRouter);

Now /users/:userId/posts/... hits postsRouter. Useful for nested resources.

Separation of Concerns

Routes declare endpoints. Controllers handle logic. The router file imports controllers and binds them:

// routes/users.js
const { listUsers, createUser, getUser } = require('../controllers/userController');
router.get('/', listUsers);

The router file stays thin and declarative.

The Takeaway

express.Router lets you group routes by feature in separate files, mount them under a path in app.js, apply per-router middlewares, and nest routers for nested resources. Use it from day one to keep app.js clean.