What is the difference between NestJS and Express.js in terms of architecture?

NestJS and Express.js are two popular frameworks in Node.js based backend development, but they have significant differences in terms of architecture:

1. Architecture

• Express.js:

  • Minimalist and Flexible: Express.js is a minimalist framework that provides only the basic features to build web applications and APIs. Its architecture does not require users to follow a specific pattern or structure, thus giving developers full flexibility to design and organize applications as needed.

  • No Built-in Structure: Express does not enforce any particular architectural pattern. Developers are free to organize their application folders, files, and flows however they like. However, this also means that developers must manually implement the required structures and patterns.

• NestJS:

  • Opinionated and Modular: NestJS is a very opinionated framework with a modular-based architecture and concepts similar to Angular (dependency injection, decorators, modules, services). NestJS is built on top of Express (or Fastify) and follows the MVC (Model-View-Controller) architectural pattern and modularity.

  • Based on Layered and Modular Architecture: NestJS enforces a modular application structure where code is grouped into separate modules. Each module can have associated controllers, services, and providers, making the application more organized and scalable.

2. Dependency Injection

• Express.js:

  • No Built-in Dependency Injection: Express.js does not have a built-in dependency injection (DI) system. Developers must manage dependencies manually, for example by using the singleton or module pattern.

• NestJS:

  • Built-in Dependency Injection (DI): NestJS has a powerful built-in DI system, similar to the one in Angular. Dependency injection makes it easier to manage dependencies, improves testability, and makes code more modular.

3. Decorators and Annotations

• Express.js:

  • No Decorators: Express.js does not use decorators or annotations. All logic is controlled through manually written middleware, handlers, or routers.

• NestJS:

  • Using Decorators: NestJS heavily uses decorators to define controllers, routes, middleware, guards, and more. This makes the code more declarative and easy to read.

4. Approaches in Development

• Express.js:

  • Free and Fast Approach: It is suitable for small and simple projects, where you only need a basic API server. Because of its flexibility, Express is often used to build prototypes or applications with loose architectural requirements.

• NestJS:

  • Structured Approach: Better suited for large or enterprise-level projects that require a structured and scalable architecture. NestJS encourages better development practices through strict architecture and the use of design patterns such as SOLID.

5. Learning Curve

• Express.js: Due to its simplicity, Express has a low learning curve. Developers who are new to Node.js often start with Express..

• NestJS: Due to its complexity and many built-in features, NestJS has a higher learning curve, especially for those who are not familiar with the concepts of modularity and dependency injection.

Conclusion

• Express.js is more suitable for projects that require high flexibility, fast build, and do not require complex architectural structures.

• NestJS is better suited for large-scale projects with the need for structured, modular, and scalable architecture.