# Dev Express Guide

> Développement d'APIs Node.js avec Express, middleware, routing, gestion d'erreurs, authentification et bonnes pratiques de conception. Se déclenche avec "Express", "Express.js", "middleware Express", "Node.js API", "router Express". Also triggers on "Express API", "Node.js middleware", "Express error handling".

- Skill: `khalilbenaz/dev-express-guide` (Agent Skill)
- Install (CLI): `npx skillmds@latest add khalilbenaz/dev-express-guide`
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- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Integrations & APIs
- Author: khalilbenaz (https://skillmd.com/u/khalilbenaz)
- Updated: 2026-09-21
- Page: https://skillmd.com/skills/khalilbenaz/dev-express-guide

---


# Guide Express.js

## Workflow

### 1. Initialiser le projet

```bash
mkdir my-api && cd my-api
npm init -y
npm install express helmet cors morgan compression express-rate-limit
npm install zod jsonwebtoken bcryptjs
npm install -D typescript ts-node @types/express @types/node nodemon jest supertest
```

Structure recommandée (feature-based) :
```
src/
  app.ts          ← config Express, middleware globaux
  server.ts       ← écoute HTTP + graceful shutdown
  routes/         ← index + un fichier par ressource
  controllers/    ← extraction req/res, appel service
  services/       ← logique métier (testable)
  middleware/     ← auth, validate, errorHandler
  models/         ← schémas DB (Prisma / Mongoose)
  utils/          ← helpers, logger, asyncHandler
  types/          ← interfaces TS globales
```

### 2. Configurer `app.ts` avec les middleware globaux

```ts
import express from 'express';
import helmet from 'helmet';
import cors from 'cors';
import morgan from 'morgan';
import compression from 'compression';
import rateLimit from 'express-rate-limit';
import { errorHandler } from './middleware/errorHandler';
import { router } from './routes';

const app = express();

app.use(helmet());
app.use(cors({ origin: process.env.ALLOWED_ORIGINS?.split(',') }));
app.use(express.json({ limit: '1mb' }));
app.use(morgan('combined'));
app.use(compression());
app.use(rateLimit({ windowMs: 15 * 60 * 1000, max: 100 }));

app.use('/api/v1', router);

// Error handler TOUJOURS en dernier
app.use(errorHandler);

export { app };
```

### 3. Router modulaire par ressource

```ts
// routes/users.ts
import { Router } from 'express';
import { authenticate } from '../middleware/auth';
import { validate } from '../middleware/validate';
import { createUserSchema } from '../schemas/user.schema';
import { createUser, getUserById } from '../controllers/user.controller';

const router = Router();

router.post('/', validate(createUserSchema), createUser);
router.get('/:id', authenticate, getUserById);

export { router as userRouter };
```

```ts
// routes/index.ts
import { Router } from 'express';
import { userRouter } from './users';

const router = Router();
router.use('/users', userRouter);
// router.use('/products', productRouter);
export { router };
```

### 4. Pattern controller → service

```ts
// middleware/asyncHandler.ts
import { RequestHandler } from 'express';
export const asyncHandler =
  (fn: RequestHandler): RequestHandler =>
  (req, res, next) =>
    Promise.resolve(fn(req, res, next)).catch(next);

// controllers/user.controller.ts
import { asyncHandler } from '../middleware/asyncHandler';
import { UserService } from '../services/user.service';

export const createUser = asyncHandler(async (req, res) => {
  const user = await UserService.create(req.body);
  res.status(201).json({ success: true, data: user });
});
```

```ts
// services/user.service.ts — aucune dépendance Express ici
import { prisma } from '../utils/db';
import bcrypt from 'bcryptjs';

export const UserService = {
  async create(data: CreateUserDto) {
    const hashed = await bcrypt.hash(data.password, 12);
    return prisma.user.create({ data: { ...data, password: hashed } });
  },
};
```

### 5. Validation avec Zod

```ts
// middleware/validate.ts
import { AnyZodObject } from 'zod';
import { RequestHandler } from 'express';

export const validate =
  (schema: AnyZodObject): RequestHandler =>
  (req, _res, next) => {
    const result = schema.safeParse({
      body: req.body,
      params: req.params,
      query: req.query,
    });
    if (!result.success) {
      return next({ status: 422, errors: result.error.flatten() });
    }
    req.body = result.data.body;
    next();
  };

// schemas/user.schema.ts
import { z } from 'zod';
export const createUserSchema = z.object({
  body: z.object({
    email: z.string().email(),
    password: z.string().min(8),
    name: z.string().min(2).max(100),
  }),
});
```

### 6. Gestion d'erreurs centralisée

```ts
// utils/AppError.ts
export class AppError extends Error {
  constructor(
    public message: string,
    public statusCode: number,
    public errors?: unknown
  ) {
    super(message);
  }
}

// middleware/errorHandler.ts
import { ErrorRequestHandler } from 'express';
import { AppError } from '../utils/AppError';

export const errorHandler: ErrorRequestHandler = (err, _req, res, _next) => {
  const status = err instanceof AppError ? err.statusCode : err.status ?? 500;
  res.status(status).json({
    success: false,
    message: err.message ?? 'Internal Server Error',
    errors: err.errors ?? undefined,
    ...(process.env.NODE_ENV === 'development' && { stack: err.stack }),
  });
};
```

### 7. Authentification JWT

```ts
// middleware/auth.ts
import jwt from 'jsonwebtoken';
import { RequestHandler } from 'express';
import { AppError } from '../utils/AppError';

export const authenticate: RequestHandler = (req, _res, next) => {
  const token = req.headers.authorization?.split(' ')[1];
  if (!token) throw new AppError('Unauthorized', 401);
  try {
    req.user = jwt.verify(token, process.env.JWT_SECRET!) as JwtPayload;
    next();
  } catch {
    next(new AppError('Token invalide ou expiré', 401));
  }
};
```

### 8. Graceful shutdown dans `server.ts`

```ts
import { app } from './app';
import { prisma } from './utils/db';

const server = app.listen(process.env.PORT ?? 3000, () =>
  console.log(`API up on :${process.env.PORT ?? 3000}`)
);

const shutdown = async (signal: string) => {
  console.log(`${signal} received — shutting down`);
  server.close(async () => {
    await prisma.$disconnect();
    process.exit(0);
  });
  setTimeout(() => process.exit(1), 10_000); // force kill si bloqué
};

process.on('SIGTERM', () => shutdown('SIGTERM'));
process.on('SIGINT', () => shutdown('SIGINT'));
```

### 9. Tests avec Jest + Supertest

```ts
// __tests__/users.test.ts
import request from 'supertest';
import { app } from '../src/app';

describe('POST /api/v1/users', () => {
  it('crée un utilisateur valide', async () => {
    const res = await request(app)
      .post('/api/v1/users')
      .send({ email: 'test@test.com', password: 'secret123', name: 'Alice' });
    expect(res.status).toBe(201);
    expect(res.body.success).toBe(true);
  });

  it('rejette un email invalide', async () => {
    const res = await request(app)
      .post('/api/v1/users')
      .send({ email: 'pas-un-email', password: 'secret123', name: 'Alice' });
    expect(res.status).toBe(422);
  });
});
```

## Critères de décision

| Besoin | Choix |
|---|---|
| API REST simple | Express + Zod + Prisma |
| Temps réel | Express + Socket.io ou passer à Fastify |
| Auth OAuth2/OIDC | `passport.js` + stratégies |
| Validation complexe | Zod (TS-first) > Joi |
| ORM | Prisma (TypeScript), Mongoose (MongoDB) |
| Logging structuré | `pino` + `pino-http` (plus rapide que morgan) |
| Haute performance | Envisager Fastify (3× plus rapide) |

## Anti-patterns / pièges

- **try-catch dans chaque route** — utilise `asyncHandler`, sinon une exception non catchée crash le process.
- **Logique métier dans les routes** — non testable, non réutilisable ; toujours isoler dans un service.
- **`app.use(express.json())` après les routes** — les routes ne verront pas le body parsé. L'ordre des middleware EST la logique.
- **Oublier `next(err)` dans les middleware async** — une `Promise` rejetée sans `.catch(next)` ou `asyncHandler` ne déclenche pas l'error handler.
- **`res.send()` après `res.json()`** — double send → crash. Toujours `return res.json(...)`.
- **Variables d'env en dur** — utiliser `dotenv` + valider avec `envalid` ou Zod au démarrage.
- **Pas de rate limiting** — brute force triviale sans `express-rate-limit` ou un WAF upstream.
- **Port binding dans `app.ts`** — rend les tests Supertest lents (port déjà occupé) ; séparer `app.ts` et `server.ts`.
- **Helmet désactivé en prod** — headers par défaut exposent la stack tech.

## Bonnes pratiques 2026

- **TypeScript strict** (`"strict": true`) — évite les bugs de runtime sur `req.params` / `req.query` (toujours `string`).
- **Versioning d'API** — préfixer `/api/v1/` dès le début, impossible à ajouter proprement après coup.
- **Format de réponse uniforme** — `{ success, data, error, message, meta }` sur toutes les routes, y compris erreurs.
- **Health check** — `GET /health` renvoie `{ status: "ok", uptime, db: "connected" }` pour les load balancers / k8s.
- **OpenAPI** — générer la spec avec `zod-to-openapi` ou `tsoa` pour documenter et valider les contrats.
- **`pino`** à la place de `console.log` — JSON structuré, niveaux, corrélation par `requestId`.


## Communication Rules — MANDATORY

- Ultra-concise. No filler, no preamble, no pleasantries.
- Never say "happy to help", "sure!", "great question", "let me", or similar.
- Tool first, talk second. Act before explaining.
- Result first. Lead with outcome, not process.
- Stop when done. No summary, no recap, no trailing commentary.
- No politeness wrappers. Direct and blunt.
- Minimum words. If one word works, do not use ten.
- No unsolicited explanations.
- No emoji unless asked.