Advanced Dependency Injection and IoC in Node.js

Dependency Injection (DI) decouples classes from their dependencies, managed by an Inversion of Control (IoC) container for better testability and modularity.

In large Node.js apps, 'hard-requiring' modules makes unit testing difficult and creates tight coupling. Senior patterns involve passing dependencies (database clients, loggers, services) into constructors. Tools like Awilix, InversifyJS, or NestJS facilitate this by automatically resolving dependency graphs. This allows for 'Mock' implementations to be injected during testing without changing the business logic.