04 Routing

title: Routing in Node.js REST APIs — Complete Guide weight: 14 date: 2026-06-28 lastmod: 2026-06-28 description: Master Express Router for REST APIs including route parameters, query strings, modular routing, route grouping, and nested routers for clean endpoint organization. tags: [api-development, nodejs]

Express Router enables modular route definitions for REST APIs, with support for route parameters, query string parsing, router-level middleware, and nested router mounting for clean endpoint organization.

```mermaid
flowchart TD
  A[Express Router] --> B[Router Instance]
  B --> C[router.get('/users', handler)]
  B --> D[router.post('/users', handler)]
  B --> E[router.param('id', middleware)]
  A --> F[Nested Routers]
  F --> G[app.use('/api/users', userRouter)]
  F --> H[app.use('/api/orders', orderRouter)]
  style A fill:#e1f5fe
  style B fill:#c8e6c9

The Express Router is a mini Express application that can contain middleware and routes. You create a router instance, define routes on it, and mount it on the main app at a base path. This keeps route definitions close to their related logic.

Think of Express Router like a department store directory. Each floor (router) has its own departments (routes). The main entrance (app) directs you to the right floor based on what you need.

Example: Creating and Mounting Routers

// src/routes/userRoutes.js
const express = require('express');
const router = express.Router();
const userController = require('../controllers/userController');

// GET /api/users
router.get('/', userController.listUsers);

// GET /api/users/:id
router.get('/:id', userController.getUser);

// POST /api/users
router.post('/', userController.createUser);

module.exports = router;

// src/app.js
const userRoutes = require('./routes/userRoutes');
app.use('/api/users', userRoutes);

Example: Route Parameters and Query Strings

const express = require('express');
const router = express.Router();

// Route parameter
router.get('/users/:userId/orders/:orderId', (req, res) => {
  const { userId, orderId } = req.params;
  res.json({
    message: `Fetching order ${orderId} for user ${userId}`
  });
});

// Query string
router.get('/products', (req, res) => {
  const { category, minPrice, maxPrice, sort } = req.query;
  res.json({
    filters: { category, minPrice, maxPrice },
    sort,
    message: 'Filtered products'
  });
});

// Test: GET /products?category=electronics&minPrice=100&sort=-price

Expected output:

{"filters": {"category": "electronics", "minPrice": "100"}, "sort": "-price", "message": "Filtered products"}

Example: Router-Level Middleware

const express = require('express');
const router = express.Router();

// Middleware runs for all routes in this router
router.use((req, res, next) => {
  console.log(`[User API] ${req.method} ${req.originalUrl}`);
  next();
});

// Route-specific middleware
const validateUserId = (req, res, next) => {
  const id = parseInt(req.params.id);
  if (isNaN(id) || id <= 0) {
    return res.status(400).json({ error: 'Invalid user ID' });
  }
  req.userId = id;
  next();
};

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

module.exports = router;

Common Mistakes

1. Route order sensitivity — Express matches routes in order. Place parameterized routes after static routes: /users/new before /users/:id.
2. Missing route for 404s — Add a catch-all route at the end of your router to handle undefined endpoints with a proper 404 response.
3. Overlapping route patterns — /users/:id and /users/profile conflict when profile is treated as an ID. Use specific paths or different prefixes.
4. Not using router.param() for parameter validation — router.param('id', validator) runs middleware automatically when :id is present in the route.
5. Mixing route definitions and business logic — Route handlers should be one-liners calling controller methods, not containing business logic.

Practice Questions

1. How do you create a nested route for orders under users?
2. What is the difference between req.params and req.query?
3. Why does route order matter in Express?
4. How do you add middleware to a specific route?
5. Challenge: Set up routing for a library API with nested routers for books, authors, and members. Include a route parameter for book ID and query parameters for filtering books by genre and year.

FAQ

Mini Project

Build a routing system for a blog API with the following routes: GET /posts, GET /posts/:id, GET /posts/:id/comments, POST /posts, POST /posts/:id/comments, GET /users/:userId/posts. Include query parameters for pagination and filtering on list endpoints.

What's Next

Now learn about middleware basics in Building REST APIs with Node.js.