When building scalable backend APIs with Express.js, clean project structure and proper REST principles are key.

In this blog, we’ll cover:

• Folder structure for an Express project

• REST API design using a users resource

• Proper status codes and response structure

• Visual diagrams to make it simple

📂 Folder Structure for Clean Express API

Here’s a simple but scalable structure:

project/
├── controllers/
│   └── userController.js
├── routes/
│   └── userRoutes.js
├── models/
│   └── userModel.js
├── app.js
└── server.js

• controllers/ → Handles request logic

• routes/ → Manages API endpoints

• models/ → Handles data (can be a DB model or simple array)

• app.js → Sets up Express app

• server.js → Starts the server

📦 Basic REST API for "Users" Resource

We’ll build CRUD operations:

• Create (POST) → Add user

• Read (GET) → Get all users

• Update (PUT) → Update user

• Delete (DELETE) → Remove user

1. server.js

const app = require('./app');
const PORT = 5000;

app.listen(PORT, () => console.log(`Server running on port ${PORT}`));

2. app.js

const express = require('express');
const userRoutes = require('./routes/userRoutes');

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

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

module.exports = app;

3. routes/userRoutes.js

const express = require('express');
const { getUsers, createUser, updateUser, deleteUser } = require('../controllers/userController');

const router = express.Router();

router.get('/', getUsers);
router.post('/', createUser);
router.put('/:id', updateUser);
router.delete('/:id', deleteUser);

module.exports = router;

4. controllers/userController.js

let users = [
  { id: 1, name: 'Rahul' },
  { id: 2, name: 'Sita' }
];

// GET all users
exports.getUsers = (req, res) => {
  res.status(200).json({ success: true, data: users });
};

// POST create user
exports.createUser = (req, res) => {
  const { name } = req.body;
  const newUser = { id: users.length + 1, name };
  users.push(newUser);
  res.status(201).json({ success: true, data: newUser });
};

// PUT update user
exports.updateUser = (req, res) => {
  const userId = parseInt(req.params.id);
  const { name } = req.body;

  users = users.map(user => (user.id === userId ? { ...user, name } : user));
  res.status(200).json({ success: true, message: 'User updated' });
};

// DELETE user
exports.deleteUser = (req, res) => {
  const userId = parseInt(req.params.id);
  users = users.filter(user => user.id !== userId);
  res.status(200).json({ success: true, message: 'User deleted' });
};

✅ Status Code Best Practices

• Always return clear success flags and meaningful messages.

📐 Diagram: CRUD Operations Mapping

📐 Diagram: Express API Request Flow

Client Request → Route (userRoutes.js) → Controller (userController.js) → Response

🚀 Final Thoughts

• Keep routes, controllers, and models separated for clean code.

• Use correct HTTP status codes.

• Always send consistent JSON responses.

• Start with simple resources like users to practice clean API design.