dependency-injection-design

Dependency injection in TypeScript uses interface-based design and constructor injection to isolate implementations, enabling you to easily replace real dependencies with mocks for unit testing.

A central DI container structures modular architecture by managing module interdependencies and enforcing module boundaries, using factory patterns to assemble services and register defaults systematically.

Define your AppDeps interface to establish module boundaries, create defaults using createDefaults, and assemble services using createFactory to initialize the application with registered dependencies.

Factory patterns support service creation in medium-to-large TypeScript projects by centralizing instantiation within the DI container, clarifying module boundaries, and enabling pluggable extensions via configuration schema.

Constructor injection and interface-based design are needed when you want to isolate implementations, enforce interface-based communication between modules, and ensure easy testing through mockable dependencies.