Nestjs

Services

• Services contain business logic
• Use constructor injection for dependencies
• Services should be stateless (no instance variables for request data)
• Use @Injectable() with appropriate scope (default singleton is usually correct)
• Use async/await for asynchronous operations
• Avoid unhandled promise rejections - always handle errors
• Propagate errors appropriately (don't swallow exceptions)
• Return meaningful error messages from service layer

DTOs and Validation

• Use class-validator decorators on DTO properties
• Apply ValidationPipe globally or per-route
• Use class-transformer for type transformation
• Create separate DTOs for create/update operations

Guards and Interceptors

• Guards for authentication/authorization
• Interceptors for logging, transformation, caching
• Use @UseGuards() and @UseInterceptors() decorators
• Order matters: guards run before interceptors

Error Handling

• Use built-in exceptions (NotFoundException, BadRequestException, etc.)
• Create exception filters for custom error formatting
• Don't catch and ignore errors silently

Configuration (Essential)

• Use @nestjs/config for configuration management
• Validate environment variables on startup
• Use ConfigModule.forRoot() in app module
• Access config via ConfigService dependency injection
• Don't hardcode configuration values in code

Testing

• Write unit tests using @nestjs/testing
• Mock dependencies with createMock or manual mocks
• Test controllers, services, and guards separately
• Use Test.createTestingModule() for integration tests
• Write e2e tests for critical flows
• Separate test code from implementation code

File Organization

• Follow consistent file naming (e.g., user.controller.ts, user.service.ts)
• Group related files in feature folders
• Keep modules, controllers, services, DTOs in separate files
• Use consistent folder structure across features
• Place shared/common code in dedicated folders

API Documentation (Advanced)

• Use @nestjs/swagger for automatic API documentation
• Apply @Api* decorators to controllers and DTOs
• Document all endpoints with @ApiOperation()
• Define response types with @ApiResponse()
• Include examples in @ApiProperty() decorators
• Keep Swagger docs up to date with code changes