Functional Dependency Injection Pattern

About

This skill guides developers in implementing a functional alternative to class-based services by standardizing the fn(args, deps) signature. By separating per-call arguments from long-lived infrastructure dependencies, it prevents 'god object' bloat, simplifies unit testing with automatic mocking, and ensures architectural clarity in TypeScript applications. It provides specific guidance on factory functions, type-only imports, and maintaining framework-agnostic business logic even when using frameworks like NestJS.

Key Features

• Standardized fn(args, deps) function signatures
• Framework-agnostic business logic integration for NestJS and Express
• Strangler fig migration strategies for legacy class-based code
• Strict separation of per-call data and long-lived collaborators
• Automated dependency mocking patterns with vitest-mock-extended
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Use Cases

• Implementing clean architecture with explicit dependency injection in TypeScript
• Refactoring bloated class-based services into manageable pure functions
• Improving unit test isolation and reducing boilerplate in test suites