NestJS Basics

Q: Can I use ESM with NestJS?

Yes with "type": "module" and .js extensions in imports. Check NestJS 11 ESM docs for current support status.

10 examples to understand the NestJS 11 mental model - 7 basic and 3 intermediate.

Prerequisites

npm i -g @nestjs/cli@11
nest new my-api --strict
cd my-api
npm pkg set type=module

For DI patterns and cross-cutting concerns, see Dependency Injection and Guards, Interceptors & Pipes.

Basic Examples

1. Module, Controller, Service

// users.module.ts
import { Module } from "@nestjs/common";
import { UsersController } from "./users.controller.js";
import { UsersService } from "./users.service.js";
 
@Module({
  controllers: [UsersController],
  providers: [UsersService],
})
export class UsersModule {}

// users.service.ts
import { Injectable } from "@nestjs/common";
 
@Injectable()
export class UsersService {
  findAll() {
    return [{ id: 1, name: "Ada Lovelace" }];
  }
}

// users.controller.ts
import { Controller, Get } from "@nestjs/common";
import { UsersService } from "./users.service.js";
 
@Controller("users")
export class UsersController {
  constructor(private readonly usersService: UsersService) {}
 
  @Get()
  findAll() {
    return this.usersService.findAll();
  }
}

@Module groups related controllers and providers
@Injectable marks a class for DI
@Controller defines route prefix; methods define HTTP verbs

2. Route Parameters and Body

import { Controller, Get, Post, Body, Param } from "@nestjs/common";
 
@Controller("users")
export class UsersController {
  @Get(":id")
  findOne(@Param("id") id: string) {
    return { id, name: "Ada" };
  }
 
  @Post()
  create(@Body() body: { name: string; email: string }) {
    return { id: "1", ...body };
  }
}

@Param("id") extracts route parameters
@Body() extracts request body (parsed by underlying adapter)
Add ValidationPipe for automatic validation

3. Root Module and Bootstrap

// app.module.ts
import { Module } from "@nestjs/common";
import { UsersModule } from "./users/users.module.js";
 
@Module({
  imports: [UsersModule],
})
export class AppModule {}

// main.ts
import { NestFactory } from "@nestjs/core";
import { AppModule } from "./app.module.js";
 
async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  await app.listen(process.env.PORT ?? 3000);
}
bootstrap();

AppModule is the root; import feature modules
NestFactory.create bootstraps the DI container
Use NestFactory.create(AppModule, new FastifyAdapter()) for performance

4. Global Prefix

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.setGlobalPrefix("api/v1");
  await app.listen(3000);
}

All routes prefixed with /api/v1
Health checks often excluded: setGlobalPrefix("api", { exclude: ["health"] })

5. ValidationPipe

import { ValidationPipe } from "@nestjs/common";
 
async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.useGlobalPipes(new ValidationPipe({ whitelist: true, transform: true }));
  await app.listen(3000);
}

import { IsEmail, IsString, MinLength } from "class-validator";
 
export class CreateUserDto {
  @IsString()
  @MinLength(1)
  name!: string;
 
  @IsEmail()
  email!: string;
}

whitelist: true strips unknown properties
transform: true converts plain objects to DTO class instances
Requires class-validator and class-transformer

6. Exception Filters

import { ExceptionFilter, Catch, ArgumentsHost, HttpException } from "@nestjs/common";
 
@Catch(HttpException)
export class HttpExceptionFilter implements ExceptionFilter {
  catch(exception: HttpException, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse();
    const status = exception.getStatus();
    response.status(status).json(exception.getResponse());
  }
}

Filters catch exceptions and shape error responses
@Catch(HttpException) scopes to HTTP exceptions
Register globally or per-controller

7. Environment Configuration

import { Module } from "@nestjs/common";
import { ConfigModule } from "@nestjs/config";
 
@Module({
  imports: [ConfigModule.forRoot({ isGlobal: true })],
})
export class AppModule {}

import { Injectable } from "@nestjs/common";
import { ConfigService } from "@nestjs/config";
 
@Injectable()
export class AppService {
  constructor(private config: ConfigService) {}
 
  getPort() {
    return this.config.get<number>("PORT", 3000);
  }
}

@nestjs/config loads .env files
ConfigService injects environment values
Validate env with Joi or Zod at startup

Intermediate Examples

8. Fastify Adapter

import { NestFactory } from "@nestjs/core";
import { FastifyAdapter, NestFastifyApplication } from "@nestjs/platform-fastify";
import { AppModule } from "./app.module.js";
 
async function bootstrap() {
  const app = await NestFactory.create<NestFastifyApplication>(
    AppModule,
    new FastifyAdapter({ logger: true })
  );
  await app.listen({ port: 3000, host: "0.0.0.0" });
}
bootstrap();

Fastify adapter removes Express overhead
See NestJS Performance Reality

9. Feature Module Exports

@Module({
  providers: [UsersService],
  exports: [UsersService],
})
export class UsersModule {}
 
@Module({
  imports: [UsersModule],
  controllers: [OrdersController],
})
export class OrdersModule {}
// OrdersController can inject UsersService

exports makes providers available to importing modules
Without exports, providers are private to the module

10. Lifecycle Hooks

import { Injectable, OnModuleInit, OnModuleDestroy } from "@nestjs/common";
 
@Injectable()
export class DatabaseService implements OnModuleInit, OnModuleDestroy {
  async onModuleInit() {
    console.log("Connecting to database...");
  }
 
  async onModuleDestroy() {
    console.log("Closing database connections...");
  }
}

onModuleInit runs after module dependencies are resolved
onModuleDestroy runs on graceful shutdown
Use for connection pool setup and teardown

FAQs

When should I choose NestJS over Fastify?

NestJS when you need DI, modular architecture, guards/interceptors, and microservices patterns. Fastify for lean APIs. See Framework Selection Checklist.

Is NestJS 11 production-ready?

Yes. NestJS 11 supports Express 5 and Fastify 5 adapters on Node 24 LTS.

Does NestJS require TypeScript?

Strongly recommended. NestJS is decorator-driven and designed for TypeScript. JavaScript works but loses type safety.

How does NestJS compare to Spring Boot?

Similar mental model: modules, DI, decorators, guards. NestJS is the closest Node equivalent.

Can I use ESM with NestJS?

Yes with "type": "module" and .js extensions in imports. Check NestJS 11 ESM docs for current support status.

Dependency Injection - DI patterns
Guards, Interceptors & Pipes - cross-cutting
NestJS + Prisma/TypeORM - data layer
Fastify Basics - underlying adapter
NestJS Best Practices - section checklist

NestJS Documentation - Progressive Node.js framework docs.
freeCodeCamp – Backend Development & APIs - Free certification path with Node/Express projects.
MDN Web Docs – Express/Node.js - Beginner-to-intermediate Express/Node tutorials.
Get Programming with Node.js - Introductory programming with Node.js.
Node.js in Action, 2nd Edition - Classic practical Node.js.

Stack versions: This page was written for Node.js 24.18.0 (Active LTS), npm 10+, TypeScript 5.6+, Express 5, Fastify 5, and NestJS 11.

Prerequisites

npm i -g @nestjs/cli@11
nest new my-api --strict
cd my-api
npm pkg set type=module

For DI patterns and cross-cutting concerns, see Dependency Injection and Guards, Interceptors & Pipes.

Basic Examples

1. Module, Controller, Service

// users.module.ts
import { Module } from "@nestjs/common";
import { UsersController } from "./users.controller.js";
import { UsersService } from "./users.service.js";
 
@Module({
  controllers: [UsersController],
  providers: [UsersService],
})
export class UsersModule {}

// users.service.ts
import { Injectable } from "@nestjs/common";
 
@Injectable()
export class UsersService {
  findAll() {
    return [{ id: 1, name: "Ada Lovelace" }];
  }
}

// users.controller.ts
import { Controller, Get } from "@nestjs/common";
import { UsersService } from "./users.service.js";
 
@Controller("users")
export class UsersController {
  constructor(private readonly usersService: UsersService) {}
 
  @Get()
  findAll() {
    return this.usersService.findAll();
  }
}

@Module groups related controllers and providers
@Injectable marks a class for DI
@Controller defines route prefix; methods define HTTP verbs

2. Route Parameters and Body

import { Controller, Get, Post, Body, Param } from "@nestjs/common";
 
@Controller("users")
export class UsersController {
  @Get(":id")
  findOne(@Param("id") id: string) {
    return { id, name: "Ada" };
  }
 
  @Post()
  create(@Body() body: { name: string; email: string }) {
    return { id: "1", ...body };
  }
}

@Param("id") extracts route parameters
@Body() extracts request body (parsed by underlying adapter)
Add ValidationPipe for automatic validation

3. Root Module and Bootstrap

// app.module.ts
import { Module } from "@nestjs/common";
import { UsersModule } from "./users/users.module.js";
 
@Module({
  imports: [UsersModule],
})
export class AppModule {}

// main.ts
import { NestFactory } from "@nestjs/core";
import { AppModule } from "./app.module.js";
 
async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  await app.listen(process.env.PORT ?? 3000);
}
bootstrap();

AppModule is the root; import feature modules
NestFactory.create bootstraps the DI container
Use NestFactory.create(AppModule, new FastifyAdapter()) for performance

4. Global Prefix

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.setGlobalPrefix("api/v1");
  await app.listen(3000);
}

All routes prefixed with /api/v1
Health checks often excluded: setGlobalPrefix("api", { exclude: ["health"] })

5. ValidationPipe

import { ValidationPipe } from "@nestjs/common";
 
async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.useGlobalPipes(new ValidationPipe({ whitelist: true, transform: true }));
  await app.listen(3000);
}

import { IsEmail, IsString, MinLength } from "class-validator";
 
export class CreateUserDto {
  @IsString()
  @MinLength(1)
  name!: string;
 
  @IsEmail()
  email!: string;
}

whitelist: true strips unknown properties
transform: true converts plain objects to DTO class instances
Requires class-validator and class-transformer

6. Exception Filters

import { ExceptionFilter, Catch, ArgumentsHost, HttpException } from "@nestjs/common";
 
@Catch(HttpException)
export class HttpExceptionFilter implements ExceptionFilter {
  catch(exception: HttpException, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse();
    const status = exception.getStatus();
    response.status(status).json(exception.getResponse());
  }
}

Filters catch exceptions and shape error responses
@Catch(HttpException) scopes to HTTP exceptions
Register globally or per-controller

7. Environment Configuration

import { Module } from "@nestjs/common";
import { ConfigModule } from "@nestjs/config";
 
@Module({
  imports: [ConfigModule.forRoot({ isGlobal: true })],
})
export class AppModule {}

import { Injectable } from "@nestjs/common";
import { ConfigService } from "@nestjs/config";
 
@Injectable()
export class AppService {
  constructor(private config: ConfigService) {}
 
  getPort() {
    return this.config.get<number>("PORT", 3000);
  }
}

@nestjs/config loads .env files
ConfigService injects environment values
Validate env with Joi or Zod at startup

Intermediate Examples

8. Fastify Adapter

import { NestFactory } from "@nestjs/core";
import { FastifyAdapter, NestFastifyApplication } from "@nestjs/platform-fastify";
import { AppModule } from "./app.module.js";
 
async function bootstrap() {
  const app = await NestFactory.create<NestFastifyApplication>(
    AppModule,
    new FastifyAdapter({ logger: true })
  );
  await app.listen({ port: 3000, host: "0.0.0.0" });
}
bootstrap();

Fastify adapter removes Express overhead
See NestJS Performance Reality

9. Feature Module Exports

@Module({
  providers: [UsersService],
  exports: [UsersService],
})
export class UsersModule {}
 
@Module({
  imports: [UsersModule],
  controllers: [OrdersController],
})
export class OrdersModule {}
// OrdersController can inject UsersService

exports makes providers available to importing modules
Without exports, providers are private to the module

10. Lifecycle Hooks

import { Injectable, OnModuleInit, OnModuleDestroy } from "@nestjs/common";
 
@Injectable()
export class DatabaseService implements OnModuleInit, OnModuleDestroy {
  async onModuleInit() {
    console.log("Connecting to database...");
  }
 
  async onModuleDestroy() {
    console.log("Closing database connections...");
  }
}

onModuleInit runs after module dependencies are resolved
onModuleDestroy runs on graceful shutdown
Use for connection pool setup and teardown

FAQs

When should I choose NestJS over Fastify?

NestJS when you need DI, modular architecture, guards/interceptors, and microservices patterns. Fastify for lean APIs. See Framework Selection Checklist.

Is NestJS 11 production-ready?

Yes. NestJS 11 supports Express 5 and Fastify 5 adapters on Node 24 LTS.

Does NestJS require TypeScript?

Strongly recommended. NestJS is decorator-driven and designed for TypeScript. JavaScript works but loses type safety.

How does NestJS compare to Spring Boot?

Similar mental model: modules, DI, decorators, guards. NestJS is the closest Node equivalent.

Can I use ESM with NestJS?

Yes with "type": "module" and .js extensions in imports. Check NestJS 11 ESM docs for current support status.

Dependency Injection - DI patterns
Guards, Interceptors & Pipes - cross-cutting
NestJS + Prisma/TypeORM - data layer
Fastify Basics - underlying adapter
NestJS Best Practices - section checklist

NestJS Documentation - Progressive Node.js framework docs.
freeCodeCamp – Backend Development & APIs - Free certification path with Node/Express projects.
MDN Web Docs – Express/Node.js - Beginner-to-intermediate Express/Node tutorials.
Get Programming with Node.js - Introductory programming with Node.js.
Node.js in Action, 2nd Edition - Classic practical Node.js.

Stack versions: This page was written for Node.js 24.18.0 (Active LTS), npm 10+, TypeScript 5.6+, Express 5, Fastify 5, and NestJS 11.

NestJS Basics

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NestJS Basics