Architecture and features of Nest.js

Modular Structure

Nest.js is built on a strong modular architecture that organizes code into coherent and reusable units. Every Nest.js application consists of at least one module — the root module. The standard structure includes:

• Modules: These encapsulate specific parts of the application and group related components together. Each module can import other modules and export its own providers.
• Controllers: They handle incoming requests and send responses to the client. Controllers define routes and the supported HTTP methods.
• Providers: These include services, repositories, factories, and helpers that contain the business logic. They are designed to be injected as dependencies.

Dependency injection

Dependency injection is at the core of Nest.js. This architectural pattern allows for better code organization, simplifies testing, and ensures low coupling between components.

// Exemple d'un provider (service)
@Injectable()
export class UserService {
  constructor(
    @InjectRepository(User)
    private usersRepository: Repository<User>,
  ) {}

  findAll(): Promise<User[]> {
    return this.usersRepository.find();
  }
}

// Exemple d'un contrôleur utilisant l'injection de dépendances
@Controller('users')
export class UserController {
  constructor(private readonly userService: UserService) {}

  @Get()
  findAll(): Promise<User[]> {
    return this.userService.findAll();
  }
}

Decorators and metadata

Nest.js makes extensive use of TypeScript decorators to attach metadata to classes and facilitate their handling:

• @Module() – defines a module
• @Controller() – defines a controller
• @Injectable() – marks a class as injectable (provider)
• @Get(), @Post(), etc. – define HTTP methods for routes

This declarative approach makes the code more readable and helps in understanding the different parts of the application.

Advantages of Nest.js

Opinionated Architecture and Consistent Structure

Nest.js enforces a clear structure and conventions, ensuring consistency across different parts of the application and among development teams. Unlike Express.js, which is highly flexible but can lead to disorganized codebases, Nest.js guides developers toward standardized practices.

Native TypeScript support
The framework is built with TypeScript, offering:

• Better error detection at compile time
• Enhanced autocompletion in IDEs
• Built-in code documentation through types
• Increased maintainability for large-scale projects

Comprehensive documentation

Nest.js provides extensive documentation with numerous examples and practical guides. This resource is especially helpful for new developers and facilitates quick onboarding within teams.

Rich and modular ecosystem

The framework offers a wide range of built-in and official modules for:

• Authentication and authorization
• Data validation
• Database connections (TypeORM, Mongoose, etc.)
• Microservices
• API documentation (OpenAPI/Swagger)
• WebSockets and real-time communication

This modular approach allows developers to add features without having to rebuild everything from scratch.

Support for modern architectural patterns

Nest.js natively supports:

• Hexagonal/onion architecture
• CQRS (Command Query Responsibility Segregation)
• Microservices
• Reactive programming

These patterns make it easier to build scalable and maintainable applications.

Testability
The framework is designed with testability in mind:

• Native support for Jest for unit testing
• Utilities to simplify integration tests
• Easy mocking of dependencies thanks to dependency injection

Performance and Scalability
Nest.js provides:

• A non-blocking I/O model inherited from Node.js
• Optimizations for handling concurrent requests
• The ability to use Fastify instead of Express as the HTTP layer for better performance

Disadvantages and limitations of Nest.js

Steep Learning Curve
The sophisticated architecture and heavy use of TypeScript and advanced concepts like decorators can be intimidating for beginners—especially those unfamiliar with Angular or TypeScript.

Circular Dependency Issues
One recurring issue in Nest.js applications is handling circular dependencies. These situations, where two classes depend on each other, can cause significant complications if not properly managed.

Complexity of Unit Testing
While Nest.js facilitates testing, unit test structures can become complex—particularly when a provider has multiple dependencies. This can become a bottleneck for teams, especially on large projects.

Logging Management Issues
In certain scenarios—especially during startup errors—logs can be "swallowed," making it difficult to identify the root cause of problems.

Lack of Dynamic Controllers
Unlike the flexibility available for providers, Nest.js lacks native support for dynamic controllers, which can limit route management flexibility as a project grows.

Potential Performance Overhead
The use of numerous abstractions, decorators, and middleware can introduce some performance overhead compared to lighter approaches like raw Express.js.

Architectural Rigidity
The framework’s strong opinions on code structure can sometimes feel too restrictive for projects requiring unconventional or highly specific architectures.

Why choose Nest.js

TypeScript + Node.js Combination

• Benefits from TypeScript’s type safety and maintainability
• Leverages the performance and ecosystem of Node.js

Enterprise-Oriented Architecture

• Clearly defined structure suitable for large teams
• Facilitates standardization of development practices
• Reduces friction caused by differing coding styles

Technical Scalability

• Native support for microservices
• Easily adapts to various architectures (monolithic, microservices, serverless)
• Seamless integration with modern DevOps tools

Versatility

• Supports both RESTful APIs and GraphQL
• Built-in support for WebSockets and real-time communication
• Suitable for traditional web apps, microservices, and serverless functions

JavaScript/TypeScript Talent Reusability

• Enables front-end teams (especially Angular developers) to contribute effectively to the backend
• Reduces skill fragmentation within development teams

Enterprise use cases

While specific information about companies using Nest.js is somewhat limited in public sources, the official documentation maintains a list of companies leveraging the framework at: https://docs.nestjs.com/discover/companies.

According to available research, Nest.js is particularly well-suited for:

Large-scale Enterprise Applications

• Systems with complex business logic
• Applications requiring long-term maintenance

E-commerce Applications

• Robust APIs for handling catalogs, shopping carts, and payments
• Integration with multiple third-party services

Real-time Applications

• Messaging systems
• Real-time dashboards
• Collaborative applications

Microservices

• Distributed architecture
• Independent and loosely coupled services

Conclusion

Nest.js is a robust solution for backend development in JavaScript/TypeScript, particularly well-suited for complex and scalable enterprise applications. Its opinionated structure, native TypeScript support, and modular architecture make it a smart choice for teams looking to maintain large codebases over the long term.

The framework is not without its downsides — a steep learning curve, potential circular dependency issues, and relative complexity for simpler projects are points to consider. However, these drawbacks are generally outweighed by the benefits in maintainability and scalability for larger applications.

For Angular teams or those seeking to standardize their backend development, Nest.js provides a natural transition and familiar patterns. For simpler projects or teams preferring maximum flexibility, alternatives like Express.js may still be more appropriate.

Ultimately, choosing between Nest.js and other frameworks should be driven by project complexity, team expertise, and specific architectural and scalability requirements.

Supplementary video resources