Setting Up a NestJS Project with CLI: First App and File Structure Explained

Table of Contents

1. Prerequisites
2. Installing NestJS CLI
3. Creating a New Project
4. Understanding the Project Structure
5. Running Your First NestJS Server
6. Exploring Core Files: main.ts, AppModule, AppController, and AppService
7. Summary and Next Steps

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1. Prerequisites

Before we start, make sure you have the following installed:

• Node.js (LTS version recommended): https://nodejs.org
• npm or yarn
• Basic understanding of TypeScript
• Git (optional but useful)

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2. Installing NestJS CLI

NestJS provides a powerful CLI to scaffold and manage projects efficiently.

npm i -g @nestjs/cli

To confirm installation:

nest --version

This CLI helps you:

• Generate modules, controllers, and services
• Scaffold a new project
• Run and build applications
• Test and lint your code

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3. Creating a New Project

To create a new NestJS project:

nest new my-nest-app

You’ll be prompted to choose a package manager (npm/yarn/pnpm). Pick your preference.

Once done, navigate into the project:

cd my-nest-app

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4. Understanding the Project Structure

Here’s the default project structure:

my-nest-app/
├── src/
│   ├── app.controller.ts
│   ├── app.controller.spec.ts
│   ├── app.module.ts
│   ├── app.service.ts
│   └── main.ts
├── test/
│   └── app.e2e-spec.ts
├── .eslintrc.js
├── .prettierrc
├── nest-cli.json
├── package.json
├── tsconfig.json
└── README.md

Key Files:

• main.ts – Entry point of the app, bootstraps Nest.
• app.module.ts – Root module of the app.
• app.controller.ts – Handles HTTP requests.
• app.service.ts – Business logic for the controller.

Nest uses modules to group related components, promoting modularity and separation of concerns.

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5. Running Your First NestJS Server

To start the development server:

npm run start:dev

This runs your app in development mode with hot-reloading via ts-node-dev.

Now open http://localhost:3000, and you should see:

Hello World!

This message is returned by the default AppController.

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6. Exploring Core Files

main.ts

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

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

This is the entry point of your app. It uses the Nest Factory to create and run an instance of your application.

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app.module.ts

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

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

This defines the application’s root module using the @Module() decorator.

---

app.controller.ts

import { Controller, Get } from '@nestjs/common';
import { AppService } from './app.service';

@Controller()
export class AppController {
  constructor(private readonly appService: AppService) {}

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

It defines a route (/) and maps it to the getHello() method from the AppService.

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app.service.ts

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

@Injectable()
export class AppService {
  getHello(): string {
    return 'Hello World!';
  }
}

Provides a reusable service, injected into the controller.

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7. Summary and Next Steps

We’ve successfully set up a NestJS project using the CLI, explored the project structure, and understood how a simple app runs. This foundational understanding is key to mastering the framework.