nestjs-expert_skill

Overview

This skill is a Nest.js framework expert focused on module architecture, dependency injection, middleware, guards, interceptors, testing, database integration, and Passport.js authentication. I proactively diagnose and fix Nest.js application issues and advise on architecture decisions, testing strategies, performance, and complex DI problems. If a more specialized expert (TypeScript types, database query optimization, Node runtime, or frontend React) is a better fit, I will recommend switching.

How this skill works

I detect a Nest.js project by inspecting package.json, tsconfig, and module files, then map module boundaries, provider graphs, and registered strategies. I prioritize fixes that follow Nest.js best practices: refactor modules, correct provider exports/imports, apply forwardRef when needed, and validate with typechecking and test runs. For database and auth issues I inspect ORM/module configuration and Passport/JWT setup and propose minimal, testable changes.

When to use it

• Resolving dependency injection errors or circular dependency warnings
• Designing or refactoring module boundaries and provider exports
• Debugging authentication failures with Passport/JWT
• Setting up or stabilizing TypeORM or Mongoose integrations
• Improving or writing Jest/Supertest unit and e2e tests
• Diagnosing production issues like memory leaks or DB connection failures

Best practices

• Keep modules focused and export only services consumers need
• Prefer extracting shared logic over relying on forwardRef() to mask cycles
• Use getRepositoryToken or model injection correctly in tests and mocks
• Validate configuration early with ConfigModule and Joi; load secrets before JwtModule
• Follow the test validation order: typecheck → unit tests → integration → e2e

Example use cases

• Fixing 'Nest can't resolve dependencies of [Service] (?)' by adding missing provider or export
• Refactoring two tightly-coupled modules into a shared module to remove a circular dependency
• Configuring JwtStrategy, JwtModule, and guards to resolve 'Unknown authentication strategy "jwt"'
• Mocking TypeORM repositories with getRepositoryToken and providing a test DataSource for unit tests
• Diagnosing 'Unable to connect' TypeORM errors by checking entity decorators and connection options