Understanding NestJS Architecture: A Beginner's Guide

1. Introduction

NestJS is a progressive Node.js framework used to build efficient, scalable and maintainable server-side applications.

It is primarily built using TypeScript and provides a structured architecture for developing backend applications.

Unlike Express.js, which provides a minimal and flexible structure, NestJS follows a modular architecture that helps developers organize application code into separate components.

2. Why Do We Need NestJS Architecture?

Consider building an Instagram-like application. It requires several backend functionalities:

• User registration and authentication
• Creating and managing posts
• Following users
• Liking posts
• Managing comments
• Retrieving user feeds

Writing all these functionalities inside a single file makes the application difficult to maintain and debug.

NestJS solves this problem by organizing the application into separate modules, controllers and providers.

3. Main Components of NestJS Architecture

Modules

Modules organize related application components into logical groups.

Controllers

Controllers handle incoming HTTP requests and define API endpoints.

Providers and Services

Providers are injectable components managed by NestJS. Services commonly contain business logic.

Dependency Injection

Dependency Injection allows classes to receive their required dependencies without manually creating them.

4. Basic NestJS Architecture

A typical NestJS application follows this structure:

Client → Controller → Service → Database

• The client sends an HTTP request.
• The controller receives the request.
• The service executes business logic.
• The database stores or retrieves information.
• The response is returned to the client.

5. NestJS vs Express.js

Express.js provides a minimal framework where developers organize their application according to their preferences.

NestJS provides a predefined architectural structure using modules, controllers, providers and dependency injection.

Both frameworks can build REST APIs, but NestJS provides more built-in architectural conventions.

6. Conclusion

NestJS architecture helps developers build backend applications with better organization, maintainability, scalability and separation of responsibilities.

Understanding modules, controllers, providers and dependency injection is the foundation for learning NestJS effectively.