In a typical beginner setup, we often place all logic (server configuration, routes, database connection) inside a single file like index.ts.
But as your project grows, this becomes:
-
🧹 Messy
-
😰 Hard to manage
-
👎 Against best practices like Single Responsibility Principle
🧨 Current Problem: Everything in index.ts
// index.ts
import * as express from ‘express’;
import * as mongoose from ‘mongoose’;
import { getEnvironmentVariables } from ‘./environments/env’;
const app = express();
app.listen(5000, () => {
console.log(‘Server is running’);
});
// DB Connection Logic
const DB_URI = getEnvironmentVariables().db_url;
mongoose.connect(DB_URI, { dbName: ‘test’ })
.then(() => console.log(‘✅ MongoDB connected’))
.catch(err => console.error(‘❌ Mongo Error:’, err.message));
// Route Handlers
app.get(‘/login’, (req, res) => res.send(‘Login logic’));
app.get(‘/test’, (req, res) => res.send(‘Test route’));
This is fine for learning, but not scalable or clean.
✅ Goal: A Clean, Modular Project Structure
We’ll split responsibilities into separate files and folders:
-
server.ts→ App logic & server startup -
routes/→ Route definitions -
controllers/→ Handle request logic -
index.ts→ Entry point
🛠 Step-by-Step Refactoring
📁 1. Create server.ts
Handles:
-
MongoDB connection
-
Route registration
// server.ts
import * as express from ‘express’;
import * as mongoose from ‘mongoose’;
import { getEnvironmentVariables } from ‘./environments/env’;
import UserRouter from ‘./routes/UserRouter’;
export class Server {
public app: express.Application = express();
constructor() {
this.setConfigurations();
this.setRoutes();
}
setConfigurations() {
this.connectMongoDb();
}
connectMongoDb() {
const DB_URI = getEnvironmentVariables().db_url;
mongoose.connect(DB_URI, { dbName: ‘test’ })
.then(() => console.log(‘✅ MongoDB connected successfully’))
.catch(err => {
console.error(‘❌ MongoDB connection error:’, err.message);
process.exit(1);
});
mongoose.connection.on(‘connected’, () => {
console.log(‘Mongoose connected to DB’);
});
mongoose.connection.on(‘error’, (err) => {
console.log(‘Mongoose connection error:’, err);
});
mongoose.connection.on(‘disconnected’, () => {
console.log(‘Mongoose disconnected’);
});
}
setRoutes() {
this.app.use(‘/api/user’, UserRouter); // all user-related routes
}
}
📁 2. Create routes/UserRouter.ts
Handles:
-
Route paths (
/login,/signup) -
Forwards logic to controllers
// routes/UserRouter.ts
import { Router } from ‘express’;
import { UserController } from ‘../controllers/UserController’;
export class UserRouter {
public router: Router;
constructor() {
this.router = Router();
this.getRoutes();
this.postRoutes();
this.patchRoutes();
this.deleteRoutes();
}
getRoutes() {
this.router.get(‘/login’, UserController.login);
}
postRoutes() {}
patchRoutes() {}
deleteRoutes() {}
}
export default new UserRouter().router;
📁 3. Create controllers/UserController.ts
Handles:
-
Request → Response logic (business logic)
// controllers/UserController.ts
export class UserController {
static login(req, res) {
res.send(‘We are here to login’);
}
}
🟢 4. Update index.ts
Entry point for your project. Simple and clean.
// index.ts
import { Server } from ‘./server’;
const server = new Server().app;
const port = 5000;
server.listen(port, () => {
console.log(`🚀 Server is running on port ${port}`);
});
📦 Final Project Structure
nodejs-project/ ├── node_modules/ ├── src/ │ ├── controllers/ │ │ └── UserController.ts │ ├── environments/ │ │ ├── dev.env.ts │ │ ├── env.ts │ │ └── prod.env.ts │ ├── routes/ │ │ └── UserRouter.ts │ ├── server.ts │ └── index.ts ├── package.json ├── package-lock.json └── tsconfig.json
🔍 Testing Your Refactored API
Use Postman or browser:
GET Request to:
http://localhost:5000/api/user/login
✅ Output:
We are here to login
🧠 Visual Flow Diagram
index.ts ↓ server.ts → configures Express + MongoDB ↓ routes/UserRouter.ts → defines /login route ↓ controllers/UserController.ts → handles actual login logic
✨ Benefits of This Structure
✅ Follows Single Responsibility Principle
✅ Clean separation of concerns
✅ Easy to scale with new features (like auth, admin, product, etc.)
✅ Understandable and maintainable for any developer