nodejs-backend

Node.js Backend Skill

---

Project Structure

project/
├── src/
│   ├── core/                   # Pure business logic
│   │   ├── types.ts            # Domain types
│   │   ├── errors.ts           # Domain errors
│   │   └── services/           # Pure functions
│   │       ├── user.ts
│   │       └── order.ts
│   ├── infra/                  # Side effects
│   │   ├── http/               # HTTP layer
│   │   │   ├── server.ts       # Server setup
│   │   │   ├── routes/         # Route handlers
│   │   │   └── middleware/     # Express middleware
│   │   ├── db/                 # Database
│   │   │   ├── client.ts       # DB connection
│   │   │   ├── repositories/   # Data access
│   │   │   └── migrations/     # Schema migrations
│   │   └── external/           # Third-party APIs
│   ├── config/                 # Configuration
│   │   └── index.ts            # Env vars, validated
│   └── index.ts                # Entry point
├── tests/
│   ├── unit/
│   └── integration/
├── package.json
└── CLAUDE.md

---

API Design

Route Handler Pattern

// routes/users.ts
import { Router } from 'express';
import { z } from 'zod';
import { createUser } from '../../core/services/user';
import { UserRepository } from '../db/repositories/user';

const CreateUserSchema = z.object({
  email: z.string().email(),
  name: z.string().min(1).max(100),
});

export function createUserRoutes(userRepo: UserRepository): Router {
  const router = Router();

  router.post('/', async (req, res, next) => {
    try {
      const input = CreateUserSchema.parse(req.body);
      const user = await createUser(input, userRepo);
      res.status(201).json(user);
    } catch (error) {
      next(error);
    }
  });

  return router;
}

Dependency Injection at Composition Root

// index.ts
import { createApp } from './infra/http/server';
import { createDbClient } from './infra/db/client';
import { UserRepository } from './infra/db/repositories/user';
import { createUserRoutes } from './infra/http/routes/users';

async function main(): Promise<void> {
  const db = await createDbClient();
  const userRepo = new UserRepository(db);
  
  const app = createApp({
    userRoutes: createUserRoutes(userRepo),
  });
  
  app.listen(3000);
}