Backend Development with NestJS: Best Practices

NestJS has become a go-to framework for many developers looking to build robust, scalable, and maintainable backend systems. Designed around TypeScript, it leverages powerful architectural patterns like Dependency Injection (DI) and modular organization to simplify the development process. Whether you’re a seasoned developer or just starting with NestJS, adopting best practices can significantly enhance your productivity and code quality. In this blog post, we’ll explore some essential tips to streamline backend development with NestJS.

1. Leverage Modules for Organization

NestJS operates on a modular architecture, which encourages developers to divide application features into separate, reusable modules. Here’s why it’s beneficial:

• Scalability: Each module encapsulates related functionality, making it easier to scale.
• Reusability: Modules can be reused across different parts of the application or even different projects.
• Readability: Logical separation improves code clarity.

Example:

@Module({
  imports: [],
  controllers: [UsersController],
  providers: [UsersService],
})
export class UsersModule {}

Organize modules by feature, and consider grouping related modules into directories for larger applications.

2. Use Dependency Injection Effectively

NestJS’s built-in DI system simplifies managing dependencies. To maximize its benefits:

• Inject Services in Constructors: Avoid creating new instances manually; instead, let NestJS handle it for you.
• Use Interfaces: Define and inject interfaces for services to improve testability and flexibility.

Example:

@Injectable()
export class UsersService {
  constructor(private readonly userRepository: UserRepository) {}

  findAll() {
    return this.userRepository.findAll();
  }
}

3. Adopt DTOs and Validation

Data Transfer Objects (DTOs) define the shape of the data expected in requests, ensuring consistency and maintainability. Combine them with validation pipes to automatically validate input data.

Example:

export class CreateUserDto {
  @IsString()
  @IsNotEmpty()
  readonly name: string;

  @IsEmail()
  readonly email: string;
}

@Controller('users')
export class UsersController {
  @Post()
  create(@Body() createUserDto: CreateUserDto) {
    return this.usersService.create(createUserDto);
  }
}

Validation pipes can be globally enabled to enforce validation across the application:

app.useGlobalPipes(new ValidationPipe());

4. Utilize Middleware and Guards

Middleware and guards help manage cross-cutting concerns like authentication and logging.

• Middleware: Used for request transformations or logging.
• Guards: Enforce authorization and access control.

Example Middleware:

@Injectable()
export class LoggerMiddleware implements NestMiddleware {
  use(req: Request, res: Response, next: NextFunction) {
    console.log(req.method + ' ' + req.url);
    next();
  }
}

Example Guard:

@Injectable()
export class AuthGuard implements CanActivate {
  canActivate(context: ExecutionContext): boolean {
    const request = context.switchToHttp().getRequest();
    return request.headers.authorization === 'valid-token';
  }
}

5. Enable Global Error Handling

Centralized error handling ensures consistent error responses across your application.

Example:

@Injectable()
export class AllExceptionsFilter implements ExceptionFilter {
  catch(exception: unknown, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse<Response>();
    const status = exception instanceof HttpException
      ? exception.getStatus()
      : HttpStatus.INTERNAL_SERVER_ERROR;

    response.status(status).json({
      statusCode: status,
      message: exception instanceof HttpException ? exception.getResponse() : 'Internal server error',
    });
  }
}

app.useGlobalFilters(new AllExceptionsFilter());

6. Leverage TypeORM or Prisma for Database Access

NestJS integrates seamlessly with ORMs like TypeORM and Prisma, which streamline database interactions.

• TypeORM: Works well with relational databases and includes decorators for models.
• Prisma: A modern ORM with a schema-first approach and excellent performance.

TypeORM Example:

@Entity()
export class User {
  @PrimaryGeneratedColumn()
  id: number;

  @Column()
  name: string;

  @Column()
  email: string;
}

@Injectable()
export class UserRepository {
  constructor(@InjectRepository(User) private repo: Repository<User>) {}
}

7. Implement Testing Strategies

Testing is critical for ensuring reliability and maintainability. NestJS’s testing utilities make it straightforward to write unit and integration tests.

• Unit Tests: Focus on isolated functionality, mocking dependencies.
• Integration Tests: Validate interactions between modules.

Example:

describe('UsersService', () => {
  let service: UsersService;
  let repo: Repository<User>;

  beforeEach(async () => {
    const module = await Test.createTestingModule({
      providers: [
        UsersService,
        { provide: getRepositoryToken(User), useValue: mockRepository },
      ],
    }).compile();

    service = module.get<UsersService>(UsersService);
  });

  it('should return all users', async () => {
    const result = await service.findAll();
    expect(result).toEqual(mockUsers);
  });
});

Conclusion

NestJS provides a powerful framework for building scalable and maintainable backend systems. By following these best practices—leveraging modules, using Dependency Injection, adopting DTOs and validation, and implementing robust error handling—you can streamline your development process and ensure high-quality results. Embrace these tips in your next project, and you’ll unlock the full potential of NestJS.