refactor-nestjs_skill

Overview

This skill refactors NestJS and TypeScript server-side code to improve maintainability, readability, and adherence to SOLID principles. It identifies and resolves circular dependencies, god-object services, fat controllers, deep nesting, and SRP violations, then applies proven NestJS patterns to produce clean, testable implementations.

How this skill works

I analyze the codebase to detect dependency cycles, large services, duplicated logic, and missing architectural patterns. Refactors are planned and executed incrementally: extract responsibilities into modules, repositories, services, guards, pipes, interceptors, DTOs, and exception filters, and introduce CQRS or event-driven flows where appropriate. Tests and documentation updates accompany each change to prevent regressions and communicate breaking changes.

When to use it

• Codebase exhibits circular imports or runtime dependency errors
• Controllers contain business logic or services have too many responsibilities
• High technical debt: duplicated code, deep nesting, or large functions
• You need to introduce DTO validation, exception handling, or request-scoped data
• Preparing code for scale, microservices, or CQRS/event-driven design

Best practices

• Break features into focused feature modules and export only needed providers
• Keep controllers thin; move business logic to services and data access to repositories
• Use DTOs with class-validator/class-transformer and global or controller-level pipes
• Prefer early returns and guard clauses to avoid deep nesting
• Introduce interceptors for cross-cutting concerns and exception filters for consistent error responses
• Apply provider scopes judiciously; avoid injecting request-scoped providers into singletons

Example use cases

• Split a monolithic UserService into UserService, UserRepository, and UserMapper to enforce SRP
• Resolve circular module imports by extracting shared contracts and using forwardRef only when unavoidable
• Convert fat controller endpoints into commands/queries using NestJS CQRS for complex workflows
• Introduce ValidationPipe+DTOs and a global AllExceptionsFilter to standardize API errors
• Replace duplicated auditing logic with a LoggingInterceptor and a reusable AuditService