What is NestJS?

NestJS is a backend framework for building scalable, and reliable server-side applications in TypeScript (Angular) or JavaScript. NestJS utilizes TypeScript's features such as decorators, interfaces, and dependency injection to provide a more structured and maintainable tool for developers.

How NestJS works?

NestJS as any software development framework works by providing a structured and modular environment for building backend applications. NestJS use programing languages of TypeScript and JavaScript. It leverages various programming concepts and patterns to facilitate the development process including and elements of OOP (Object Oriented Programming), FP (Functional Programming), and FRP (Functional Reactive Programming)

Basic features of NestJS:

1. Modular Architecture: NestJS applications are organized into modules, which encapsulate related functionality. Modules contain controllers, services, and other components necessary for specific features or domains within the application.

2. Dependency Injection: NestJS utilizes a powerful dependency injection (DI) system to manage the creation and injection of dependencies into components such as controllers, services, and middleware. Dependencies defined as providers and can be injected into components using constructor injection or property injection. This promotes loose coupling between components and facilitates testing and maintenance.

3. Controllers and Routes: Controllers in NestJS are responsible for handling incoming HTTP requests and generating responses. Each controller defines a set of routes, which map HTTP request methods (GET, POST, PUT, DELETE, etc.) to corresponding controller methods (actions). Routes are defined using decorators such as @Get, @Post, @Put, @Delete, etc., making it easy to declare routes and handle different types of requests.

4. Services: Services in NestJS encapsulate business logic and data manipulation tasks. They are typically injected into controllers or other services and are responsible for performing specific tasks, such as interacting with databases, making API calls, or performing calculations. Services promote code reuse and maintainability by encapsulating common functionality in a modular and testable manner.

5. Middleware: Middleware functions in NestJS are used to intercept incoming HTTP requests and responses. Middleware can be used for tasks such as logging, authentication, authorization, error handling, and request processing. NestJS provides built-in middleware and allows developers to define custom middleware functions to address specific application requirements.

6. Interceptors: Interceptors in NestJS are used to intercept incoming requests and outgoing responses. They can be used to modify request/response objects, perform logging, handle errors, and apply cross-cutting concerns such as caching or validation. Interceptors can be applied globally to all routes or selectively to specific controllers or routes.

7. Providers and Injection Tokens: Providers in NestJS are classes or values that can be injected into other components using dependency injection. Providers are defined using classes, factories, or values and are registered within modules. NestJS also supports injection tokens, which allow for more flexible and dynamic injection of dependencies.

8. Lifecycle Hooks: NestJS provides lifecycle hooks that allow developers to execute code at different stages of the application lifecycle. These hooks include onModuleInit, onModuleDestroy, onApplicationBootstrap, onApplicationShutdown, etc., and can be used to perform initialization, cleanup, or other tasks as needed.

What can be built with NestJS?

Thanks to NestJS modular and extensible architecture, it can be used to develop a wide range of applications and services, including:

1. RESTful APIs: NestJS is commonly used to build RESTful APIs for web and mobile applications. Its built-in support for decorators, controllers, and middleware makes it easy to define and organize API endpoints.

2. GraphQL APIs: NestJS also supports GraphQL, a query language for APIs that allows clients to request only the data they need. Using libraries like @nestjs/graphql, you can create GraphQL APIs with NestJS and take advantage of features like type safety and automatic documentation.

3. Real-time applications: NestJS can be used to build real-time applications using technologies like WebSockets. With libraries like @nestjs/websockets, you can easily create WebSocket endpoints and handle bi-directional communication between clients and servers.

4. Microservices: NestJS is well-suited for building microservices architectures, where applications are composed of small, independent services that communicate with each other over the network. With built-in support for microservices patterns like message-based communication and service discovery, NestJS simplifies the development of distributed systems.

5. Server-side rendering (SSR): NestJS can be used to build server-side rendered applications, where HTML is generated on the server and sent to the client, improving performance and SEO. With libraries like @nestjs/platform-express, you can integrate NestJS with frameworks like Express.js to implement SSR.

6. Authentication and authorization: NestJS provides built-in support for implementing authentication mechanisms, such as JWT (JSON Web Tokens), OAuth, and session-based authentication. You can easily integrate NestJS with auth providers like Auth0 or implement custom solutions.

7. Task scheduling: NestJS can be used to build applications that require task scheduling or background processing, such as cron jobs or message queues. With libraries like @nestjs/schedule or @nestjs/bull, you can schedule tasks to run at specific times or process messages asynchronously.

8. Data processing pipelines: NestJS can be used to build data pipelines for tasks like ETL (extract, transform, load), data validation, or data aggregation. With libraries like @nestjs/event-emitter or @nestjs/cqrs, you can implement event-driven architectures and build complex data processing workflows.

What are downsides of AngularJS?

1. Learning Curve: NestJS follows a modular architecture and heavily relies on decorators, TypeScript, and concepts from Angular, which can have a steeper learning curve for developers who are not familiar with these technologies.

2. Opinionated: NestJS has its own conventions and best practices, which may not always align with the preferences or requirements of every project or developer.

3. Performance Overhead: Due to its layered architecture and use of decorators, NestJS may introduce some performance overhead compared to more lightweight frameworks, like Vue or React Native.

4. Dependency on TypeScript: While TypeScript offers many advantages, including type safety and improved developer experience, it also requires developers to be proficient in TypeScript.

5. Community and Ecosystem: Although NestJS has a growing community and ecosystem, it may not be as large or mature as some other frameworks, like Django, Ruby or ASP.NET

6. Overhead for Small Projects: For very small or simple projects, the additional structure and boilerplate provided by NestJS may be unnecessary and could introduce unnecessary complexity.

7. Learning Angular Concepts: While knowledge of Angular concepts can be beneficial for working with NestJS, it can also be a downside for developers who prefer other frontend frameworks or have no experience with Angular.