NestJS Framework

NestJS Framework Skill

Quick Reference

When to Use: Building scalable Node.js/TypeScript backend applications with modular architecture

Core Strengths: Dependency injection, modular design, enterprise patterns, comprehensive testing

Target Coverage: Services ≥80%, Controllers ≥70%, E2E ≥60%, Overall ≥75%

Essential Patterns

Module Architecture

// users/users.module.ts
@Module({
  imports: [TypeOrmModule.forFeature([User]), AuthModule],
  controllers: [UserController],
  providers: [
    UserService,
    UserRepository,
    { provide: 'USER_REPOSITORY', useClass: UserRepository },
  ],
  exports: [UserService],
})
export class UsersModule {}

Key Principles:

• Clear module boundaries and responsibilities
• Export only what other modules need
• Import shared modules (AuthModule, DatabaseModule)
• Use token-based providers for abstraction

Dependency Injection

// users/services/user.service.ts
@Injectable()
export class UserService {
  constructor(
    @Inject('USER_REPOSITORY') private readonly userRepository: UserRepository,
    private readonly hashingService: HashingService,
    private readonly eventEmitter: EventEmitter2,
  ) {}

  async createUser(dto: CreateUserDto): Promise<User> {
    const hashedPassword = await this.hashingService.hash(dto.password);
    const user = await this.userRepository.create({
      ...dto,
      password: hashedPassword,
    });
    this.eventEmitter.emit('user.created', user);
    return user;
  }
}

Best Practices:

• Use constructor injection for all dependencies
• Inject interfaces/tokens, not concrete implementations
• Keep services focused on single responsibility
• Emit events for cross-cutting concerns

DTO Validation

// users/dto/create-user.dto.ts
export class CreateUserDto {
  @ApiProperty({ example: '[email protected]' })
  @IsEmail({}, { message: 'Invalid email format' })
  email: string;

  @ApiProperty({ example: 'StrongP@ss123', minLength: 8 })
  @IsString()
  @MinLength(8)
  @Matches(/^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])/, {
    message: 'Password must contain uppercase, lowercase, number, symbol'
  })
  password: string;

  @ApiProperty({ example: 'John Doe', required: false })
  @IsOptional()
  @MaxLength(100)
  name?: string;
}