Express.js Guide

Applies to: Express.js 4.x/5.x, TypeScript/JavaScript, REST APIs, Web Servers, Microservices

Core Principles

1. Middleware-Centric: Everything is middleware -- parsing, auth, logging, errors
2. Layered Architecture: Controllers -> Services -> Repositories (separation of concerns)
3. Type Safety: Use TypeScript for all new Express projects
4. Security First: helmet, cors, rate limiting, input validation on every route
5. Graceful Lifecycle: Handle startup, shutdown, and uncaught errors properly

Guardrails

Project Setup

• Use TypeScript with strict mode enabled
• Install core security packages: helmet, cors, express-rate-limit
• Use dotenv for environment configuration (never hardcode secrets)