Express.js Routing & Controllers - Structuring Scalable MVC Web Applications

In production backend applications containing dozens or hundreds of endpoints, defining all routes inside a single server.js file leads to unmaintainable spaghetti code. Professional developers separate routing logic into dedicated Router files and encapsulate business operations inside Controller classes following the MVC (Model-View-Controller) architecture.

Structuring a Professional Express Project

my-api/
├── controllers/
│   └── studentController.js   // Business logic & response handling
├── routes/
│   └── studentRoutes.js       // URL route endpoints definition
├── models/
│   └── studentModel.js        // Database schema
├── middleware/
│   └── authMiddleware.js      // JWT / API key verification
└── server.js                  // App initialization & mounting

1. Defining the Controller: studentController.js

// controllers/studentController.js

// Simulated in-memory database
let students = [
  { id: 1, name: 'Amit Kumar', rollNo: 'BCA-101', course: 'Computer Science' },
  { id: 2, name: 'Priya Sharma', rollNo: 'BCA-102', course: 'Information Technology' }
];

// GET /api/students - List all students
exports.getAllStudents = (req, res) => {
  res.status(200).json({
    success: true,
    count: students.length,
    data: students
  });
};

// GET /api/students/:id - Get single student by ID
exports.getStudentById = (req, res) => {
  const studentId = parseInt(req.params.id);
  const student = students.find(s => s.id === studentId);

  if (!student) {
    return res.status(404).json({ success: false, error: 'Student not found' });
  }

  res.status(200).json({ success: true, data: student });
};

// POST /api/students - Create new student
exports.createStudent = (req, res) => {
  const { name, rollNo, course } = req.body;

  if (!name || !rollNo) {
    return res.status(400).json({ success: false, error: 'Name and RollNo are required' });
  }

  const newStudent = { id: students.length + 1, name, rollNo, course: course || 'BCA' };
  students.push(newStudent);

  res.status(201).json({ success: true, data: newStudent });
};

2. Defining the Router: studentRoutes.js

// routes/studentRoutes.js
const express = require('express');
const router = express.Router();
const studentController = require('../controllers/studentController');

// Route Chaining using router.route()
router
  .route('/')
  .get(studentController.getAllStudents)
  .post(studentController.createStudent);

router
  .route('/:id')
  .get(studentController.getStudentById);

module.exports = router;

3. Mounting the Router in server.js

// server.js
const express = require('express');
const studentRoutes = require('./routes/studentRoutes');

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

// Mount router under the /api/students path prefix
app.use('/api/students', studentRoutes);

app.listen(3000, () => console.log('Server running on port 3000'));