📘 NestJS Blog Series – Series 1

🛠️ Bootstrapping a NestJS App & Understanding App Structure

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✅ Getting Started with nest new todoApp

We create a new NestJS project using the CLI:

nest new todoApp

This sets up a clean TypeScript backend with:

• A modular structure
• TypeScript out of the box
• Preconfigured build and test tools

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📁 Project Structure Overview

After generating the app, you’ll see this:

src/
├── app.controller.ts
├── app.module.ts
├── app.service.ts
├── main.ts

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🚀 main.ts – The Entry Point

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  await app.listen(process.env.PORT ?? 3000);
}
bootstrap();

🔍 What is NestFactory?

• NestFactory is a helper class that bootstraps the NestJS application.
• Under the hood, it sets up the HTTP server (based on Express by default).
• You can swap it for Fastify if needed.

const app = await NestFactory.create(AppModule);

This creates an instance of the application using the root module AppModule.

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💡 NestFactory vs Express

Feature	Express	NestJS (with NestFactory)
Architecture	Unopinionated, DIY	Modular, opinionated
Dependency Injection	Manual	Automatic
TypeScript Support	Optional	Built-in
CLI Tools	None	Powerful scaffolding via Nest CLI
Testing	Manual	Built-in tools and patterns

NestJS builds on top of Express, giving you a framework that's structured, testable, and scalable.

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🧱 AppModule – The Root Module

import { Module } from '@nestjs/common';
import { AppController } from './app.controller';
import { AppService } from './app.service';
import { HelloModule } from './hello/hello.module';

@Module({
  imports: [HelloModule],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

🧩 What’s a Module in NestJS?

• A module is a class annotated with @Module()
• It organizes code into cohesive blocks: controllers, services, other modules

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🧩 A Feature Module Example – HelloModule

import { Module } from '@nestjs/common';
import { HelloController } from './hello.controller';
import { HelloService } from './hello.service';

@Module({
  controllers: [HelloController],
  providers: [HelloService],
  imports: [],
  exports: []
})
export class HelloModule {}

🧭 Explanation

• controllers: Handle HTTP requests
• providers: Services used by the controller or other providers
• imports: Import other modules (e.g., DatabaseModule)
• exports: Expose services to other modules if needed

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🎮 Controller – Handling HTTP Requests

import { Controller, Get, Param, Query } from '@nestjs/common';
import { HelloService } from './hello.service';

@Controller('hello')
export class HelloController {
    constructor(private readonly helloService: HelloService) {}

    @Get()
    getHello(): string {
        return this.helloService.getHello();
    }

    @Get("/name/:username")
    getUser(@Param("username") username: string): string {
        return this.helloService.getHelloWithName(username);
    }

    @Get('query')
    getHelloUser(@Query("name") name: string): string {
        return this.helloService.getHelloWithName(name);
    }
}

📌 Key Concepts

• @Controller('hello'): All routes start with /hello
• @Get(): Handles GET request to /hello
• @Param(): Gets URL parameter
• @Query(): Gets query string param like /hello/query?name=John

🔐 Constructor Injection

constructor(private readonly helloService: HelloService) {}

This uses NestJS Dependency Injection to inject the HelloService. It’s how services are shared in NestJS.

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⚙️ Service – Business Logic Layer

import { Injectable } from '@nestjs/common';

@Injectable()
export class HelloService {
    getHello(): string {
        return 'Hello nestjs';
    }

    getHelloWithName(name: string): string {
        return `Hello ${name} from nestjs`;
    }
}

💡 What is @Injectable()?

• This tells NestJS that this class can be injected into other classes.
• Think of it like @Service in Spring or a provider in Angular.

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Would you like me to generate Series 2 now with a fully working TodoModule + DTO + in-memory storage?