An introduction to Clean Architecture (also known as Onion Architecture, Hexagonal Architecture, or Ports & Adapters) applied to Node.js and TypeScript projects. The post explains the core Policy vs. Detail distinction, the Dependency Rule (inner layers must not depend on outer layers), and how using interfaces as Ports with concrete implementations as Adapters makes code both testable and flexible. Practical TypeScript code examples illustrate an email service abstraction with multiple swappable implementations (Mailchimp, SendGrid, Mailgun). The post also advises pragmatism — applying these patterns only when the complexity of the project warrants it.
