Express.js

Quick Start

import express from 'express';
import cors from 'cors';
import helmet from 'helmet';

const app = express();

app.use(helmet());
app.use(cors());
app.use(express.json());

app.get('/api/health', (req, res) => {
  res.json({ status: 'ok' });
});

app.listen(3000);

Features

Feature	Description	Guide
Project Setup	TypeScript config, middleware stack	SETUP.md
Routing	Controllers, validation, async handlers	ROUTING.md
Middleware	Auth, validation, error handling	MIDDLEWARE.md
Database	Prisma/TypeORM integration	DATABASE.md
Testing	Jest, supertest patterns	TESTING.md
Deployment	Docker, PM2, production config	DEPLOYMENT.md

Common Patterns

Controller Pattern

// controllers/users.ts
import { Request, Response, NextFunction } from 'express';
import { UserService } from '../services/UserService';

export class UserController {
  constructor(private userService: UserService) {}

  getAll = async (req: Request, res: Response, next: NextFunction) => {
    try {
      const users = await this.userService.findAll();
      res.json(users);
    } catch (error) {
      next(error);
    }
  };

  getById = async (req: Request, res: Response, next: NextFunction) => {
    try {
      const user = await this.userService.findById(req.params.id);
      if (!user) return res.status(404).json({ error: 'Not found' });
      res.json(user);
    } catch (error) {
      next(error);
    }
  };
}

Error Handler

// middleware/errorHandler.ts
import { Request, Response, NextFunction } from 'express';

export class AppError extends Error {
  constructor(
    public statusCode: number,
    message: string,
    public isOperational = true
  ) {
    super(message);
  }
}

export function errorHandler(
  err: Error,
  req: Request,
  res: Response,
  next: NextFunction
) {
  if (err instanceof AppError) {
    return res.status(err.statusCode).json({ error: err.message });
  }

  console.error(err);
  res.status(500).json({ error: 'Internal server error' });
}

Validation Middleware

// middleware/validate.ts
import { Request, Response, NextFunction } from 'express';
import { ZodSchema } from 'zod';

export function validate(schema: ZodSchema) {
  return (req: Request, res: Response, next: NextFunction) => {
    const result = schema.safeParse({
      body: req.body,
      query: req.query,
      params: req.params,
    });

    if (!result.success) {
      return res.status(400).json({ errors: result.error.issues });
    }

    next();
  };
}

Workflows

API Development Workflow

1. Define routes in routes/index.ts
2. Create controller with business logic
3. Add validation schemas with Zod
4. Write tests with supertest
5. Document with OpenAPI/Swagger

Middleware Order

1. Security (helmet, cors)
2. Rate limiting
3. Body parsing
4. Logging
5. Authentication
6. Routes
7. 404 handler
8. Error handler

Best Practices

Do	Avoid
Use async/await with try-catch	Callback patterns
Validate all inputs	Trusting client data
Use typed request/response	any types
Centralize error handling	Scattered try-catch
Use dependency injection	Direct imports in controllers

Project Structure

src/
├── app.ts              # Express setup
├── server.ts           # Server entry
├── config/             # Environment config
├── controllers/        # Route handlers
├── middleware/         # Custom middleware
├── routes/             # Route definitions
├── services/           # Business logic
├── utils/              # Helpers
└── types/              # TypeScript types

For detailed examples and patterns, see reference files above.