Code Quality Skill

• Database Patterns
• Service Patterns
• Repository Patterns

Pre-Submission Checklist

• pnpm --filter <app> lint

  passes (no ESLint rule disables).

• pnpm --filter <app> typecheck

  passes.

• pnpm --filter <app> build

  succeeds — mandatory, stricter than typecheck alone.

• pnpm --filter <app> test

  passes (new features have tests).
• Avoid

  any

  /

  unknown

  types (maintain strict type safety).
• Remove

  console.log

  statements (use a dedicated logger).
• Ensure error messages are clear and actionable.

Linting

• Command:

  pnpm lint

  (or

  pnpm lint -- --fix

  )
• Rule: NEVER disable rules with

  eslint-disable

  . Fix the underlying issue.

• @typescript-eslint/no-explicit-any

  : Define a proper interface/DTO.

• no-unused-vars

  : Remove the variable or prefix with

  _

  .

• no-console

  : Inject a

  Logger

  service.

Testing

• Unit Tests: Test individual classes (Services, Utils) with mocked dependencies.
• Integration Tests: Test interactions (Repositories) with real database/services.

describe('UserService', () => {
  it('should return user when found', async () => {
    // 1. Arrange (Mock dependencies)
    const mockRepo = { findByUid: vi.fn().mockResolvedValue(user) };  // Vitest — not jest.fn()
    const service = new UserService(mockRepo as any);
 
    // 2. Act
    const result = await service.getUser('u_1');
 
    // 3. Assert
    expect(result).toEqual(user);
    expect(mockRepo.findByUid).toHaveBeenCalledWith('u_1');
  });
});

TypeScript Type Safety

• ❌ Avoid

  any

  /

  unknown

  :
  typescript

  // BAD
  const data: any = req.body;
  
  // GOOD
  const data: CreateUserDto = req.body;

• ✅ Use DTOs and Interfaces: Always define shapes for inputs and outputs.
• ✅ Trust the Compiler: If it compiles, it should likely run (if types are accurate).

Common Anti-Patterns (General)

1. Ignoring Lint Errors: Address them immediately.
2. Logic in Controllers: Controllers should only handle HTTP req/res. Move logic to Services.
3. Hardcoded Strings/Magic Numbers: Use constants or enums.
4. Complex Conditionals: Break down complex

   if/else

   blocks into helper methods.
5. Catch-All Error Handling: Avoid just using

   console.error

   . Handle specific errors or let global filters handle them.

Related Skills

• Database Patterns: N+1 queries, Soft Deletes, Bulk Operations.
• Service Pattern NestJS: Business logic errors, Transactions.
• Repository Pattern NestJS: Data access rules.
• Backend Controller Pattern NestJS: NestJS-specific controller rules.
• Frontend Code Quality: React/Frontend specific patterns.