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NestJS Building Blocks

Organizing with Modules

Your First NestJS Module

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

@Module({
  imports: [],       // Other modules this module needs
  controllers: [AppController], // Controllers handled by this module
  providers: [AppService],   // Services (providers) available in this module
  exports: [],       // Providers to export for other modules
})
export class AppModule {}

Controllers: Handling Requests

A Simple API Endpoint

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

@Controller() // Optional path prefix, e.g., '@Controller('users')'
export class AppController {
  constructor(private readonly appService: AppService) {}

  @Get() // Handles GET requests to '/' (or '/users' if prefix exists)
  getHello(): string {
    return this.appService.getHello();
  }
}

Services: Business Logic Hub

Your Logic in a Service

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

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

Connecting the Dots

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

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  await app.listen(3000);
  console.log('NestJS application is running on http://localhost:3000');
}
bootstrap();

// When you visit http://localhost:3000,
// AppController's getHello() is called,
// which in turn calls AppService's getHello().

Component Roles Check

Core Components Summary