Injectable & DI Basics

Preview — 3 of 10 questions

Why do you decorate a service class with @Injectable()?

javascript

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

@Injectable()
export class CatsService {
  findAll(): string[] {
    return ['Felix', 'Garfield'];
  }
}

ATo make its methods static

BTo expose it as an HTTP route

CTo automatically persist it to the database

DTo mark it as a provider that the Nest DI container can manage and inject into other classes

What is the idiomatic way to inject a service into another class in NestJS?

javascript

import { Controller, Get } from '@nestjs/common';
import { CatsService } from './cats.service';

@Controller('cats')
export class CatsController {
  constructor(private readonly catsService: CatsService) {}

  @Get()
  findAll(): string[] {
    return this.catsService.findAll();
  }
}

ACall new CatsService() inside the method

BDeclare it as a private readonly constructor parameter and let Nest provide it

CImport it as a global variable

DAttach it to globalThis

You created CatsService. What must you do so it can be injected within its module?

javascript

import { Module } from '@nestjs/common';
import { CatsController } from './cats.controller';
import { CatsService } from './cats.service';

@Module({
  controllers: [CatsController],
  providers: [CatsService],
})
export class CatsModule {}

AAdd it to the module's providers array

BAdd it to the module's controllers array

CNothing — @Injectable() auto-registers it everywhere

DExport it from a barrel index.ts file

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