Fundamentals of NestJS

NestJS is a progressive Node.js framework for building efficient, reliable, and scalable server-side applications. It leverages TypeScript and is inspired by Angular, which makes it particularly appealing for developers familiar with Angular. Here are the fundamental aspects of NestJS:

Key Features of NestJS

1. TypeScript by Default
   • Definition: NestJS is built with TypeScript, providing static type-checking and other modern JavaScript features.
   • Benefits: TypeScript helps in early bug detection, better code maintainability, and improved developer productivity.
2. Modular Architecture
   • Definition: NestJS applications are divided into modules, which encapsulate related components, controllers, and providers.
   • Benefits: Modules promote code reusability, better organization, and separation of concerns.
3. Dependency Injection
   • Definition: Dependency injection is a design pattern used to manage class dependencies by injecting them rather than instantiating them directly.
   • Benefits: It enhances code testability and maintainability by decoupling the instantiation of classes from their usage.
4. Extensive Ecosystem
   • Definition: NestJS has a rich ecosystem of tools and libraries, including support for WebSockets, GraphQL, microservices, and more.
   • Benefits: This extensibility makes it suitable for a wide range of applications, from small-scale projects to enterprise-level systems.
5. Integration with Other Libraries
   • Definition: NestJS seamlessly integrates with a variety of libraries and frameworks such as Express, Fastify, TypeORM, and Mongoose.
   • Benefits: This flexibility allows developers to choose the tools that best fit their needs and preferences.

Core Concepts of NestJS

1. Modules

   • Definition: Modules are the fundamental building blocks of a NestJS application. Each module is a class annotated with a @Module() decorator.
   • Example:import { Module } from ‘@nestjs/common’;
     import { CatsController } from ‘./cats.controller’;
     import { CatsService } from ‘./cats.service’;@Module({
     controllers: [CatsController],
     providers: [CatsService],
     })
     export class CatsModule {}2. Controllers
     • Definition: Controllers handle incoming requests, delegate tasks to services, and return responses to the client. They are annotated with the @Controller() decorator.
     • Exampleimport { Controller, Get } from ‘@nestjs/common’;
       import { CatsService } from ‘./cats.service’;@Controller(‘cats’)
       export class CatsController {
       constructor(private readonly catsService: CatsService) {}@Get()
       findAll(): string {
       return this.catsService.findAll();
       }
       }

       3. Providers

       • Definition: Providers are classes that can be injected into controllers or other providers using NestJS’s dependency injection system. They are typically used to handle business logic and data manipulation.import { Injectable } from ‘@nestjs/common’;@Injectable()
         export class CatsService {
         findAll(): string {
         return ‘This action returns all cats’;
         }
         }