nestjs

NestJS

NestJS is a progressive Node.js framework for building scalable enterprise server-side applications using TypeScript, dependency injection, and modular architecture.

When to Use

• Enterprise Node.js Backend Microservices: Architecture inspired by Angular with modules, providers, and dependency injection.
• Domain-Driven Modular Applications: Structuring large codebases with clear domain separation and clean layering.
• Multi-Transport Microservices: Seamlessly switching between HTTP, gRPC, RabbitMQ, Kafka, and Redis transports.
• Type-Safe REST & GraphQL Backends: Combining TypeORM/Prisma, class-validator, and auto-generated Swagger documentation.

Quick Start

// cats.controller.ts
@Controller("cats")
export class CatsController {
  constructor(private catsService: CatsService) {}

  @Get()
  async findAll(): Promise<Cat[]> {
    return this.catsService.findAll();
  }
}

Core Concepts

Modular Architecture & Dependency Injection

Structuring modules, controllers, and injectable services:

// users.service.ts
import { Injectable, NotFoundException } from "@nestjs/common";

export interface User {
  id: string;
  email: string;
}

@Injectable()
export class UsersService {
  private users: User[] = [{ id: "1", email: "[email protected]" }];

  async findById(id: string): Promise<User> {
    const user = this.users.find((u) => u.id === id);
    if (!user) {
      throw new NotFoundException(`User with ID ${id} not found`);
    }
    return user;
  }
}

// users.controller.ts
import { Controller, Get, Param } from "@nestjs/common";

@Controller("users")
export class UsersController {
  constructor(private readonly usersService: UsersService) {}

  @Get(":id")
  async getUser(@Param("id") id: string) {
    return this.usersService.findById(id);
  }
}

Request Validation with Pipes & Class-Validator

Validating incoming JSON payloads before controller execution:

// create-user.dto.ts
import { IsEmail, IsNotEmpty, MinLength } from "class-validator";

export class CreateUserDto {
  @IsEmail({}, { message: "Invalid email address" })
  email: string;

  @IsNotEmpty()
  @MinLength(8, { message: "Password must be at least 8 characters" })
  password: string;
}

// main.ts
import { ValidationPipe } from "@nestjs/common";
import { NestFactory } from "@nestjs/core";
import { AppModule } from "./app.module";

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.useGlobalPipes(
    new ValidationPipe({
      whitelist: true, // Strip unvalidated properties
      forbidNonWhitelisted: true,
      transform: true,
    }),
  );
  await app.listen(3000);
}
bootstrap();