Express Router for Modular Routes

As your app grows, routes become messy. Router helps organize them.

The Problem

```javascript // All in one file - gets messy fast app.get('/users', ...); app.post('/users', ...); app.get('/users/:id', ...); app.get('/posts', ...); app.post('/posts', ...); app.get('/products', ...); // 100 more routes... ```

The Solution: Router

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

router.get('/', (req, res) => { res.json([{ id: 1, name: 'Alice' }]); });

router.get('/:id', (req, res) => { res.json({ id: req.params.id }); });

router.post('/', (req, res) => { res.status(201).json(req.body); });

module.exports = router; ```

```javascript // app.js const express = require('express'); const userRoutes = require('./routes/users');

const app = express(); app.use(express.json());

app.use('/api/users', userRoutes);

app.listen(3000); ```

Project Structure

``` project/ ├── app.js ├── routes/ │ ├── index.js │ ├── users.js │ ├── posts.js │ └── products.js └── package.json ```

Multiple Route Files

```javascript // routes/posts.js const router = require('express').Router();

router.get('/', (req, res) => res.json([])); router.post('/', (req, res) => res.status(201).json(req.body));

module.exports = router; ```

```javascript // routes/products.js const router = require('express').Router();

router.get('/', (req, res) => res.json([]));

module.exports = router; ```

```javascript // app.js const userRoutes = require('./routes/users'); const postRoutes = require('./routes/posts'); const productRoutes = require('./routes/products');

app.use('/api/users', userRoutes); app.use('/api/posts', postRoutes); app.use('/api/products', productRoutes); ```

Router Index File

```javascript // routes/index.js const express = require('express'); const router = express.Router();

router.use('/users', require('./users')); router.use('/posts', require('./posts')); router.use('/products', require('./products'));

module.exports = router; ```

```javascript // app.js const routes = require('./routes'); app.use('/api', routes); ```

Router-Level Middleware

```javascript // routes/admin.js const router = require('express').Router();

// Middleware for all admin routes router.use((req, res, next) => { if (!req.user?.isAdmin) { return res.status(403).json({ error: 'Admin only' }); } next(); });

router.get('/stats', (req, res) => res.json({ users: 100 })); router.delete('/users/:id', (req, res) => res.json({ deleted: true }));

module.exports = router; ```

Nested Routes

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

router.get('/', (req, res) => res.json([]));

// Nested: /api/users/:userId/posts router.get('/:userId/posts', (req, res) => { const { userId } = req.params; res.json({ userId, posts: [] }); });

module.exports = router; ```

Complete Example

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

let users = [{ id: 1, name: 'Alice' }];

router.get('/', (req, res) => { res.json(users); });

router.get('/:id', (req, res) => { const user = users.find(u => u.id === +req.params.id); if (!user) return res.status(404).json({ error: 'Not found' }); res.json(user); });

router.post('/', (req, res) => { const user = { id: users.length + 1, ...req.body }; users.push(user); res.status(201).json(user); });

router.delete('/:id', (req, res) => { users = users.filter(u => u.id !== +req.params.id); res.status(204).send(); });

module.exports = router; ```

Key Takeaway

Use `express.Router()` to split routes into separate files. Mount them with `app.use('/path', router)`. Keeps your code organized as your app grows. Each router is a mini Express app for its routes.