Provider scope (default, request, transient) in NestJS - Mini Project: Build & Apply

Understanding Provider Scope in NestJS

📖 Scenario: You are building a simple NestJS service that demonstrates how different provider scopes work. This will help you understand how NestJS manages instances of services in different scopes.

🎯 Goal: Create three services with different provider scopes: default (singleton), request-scoped, and transient. Then, inject them into a controller to observe their behavior.

📋 What You'll Learn

Create a service called DefaultService with default scope

Create a service called RequestService with request scope

Create a service called TransientService with transient scope

Inject all three services into a controller called AppController

Add a method in AppController called getScopes() that returns the instance IDs of each service

💡 Why This Matters

🌍 Real World

Understanding provider scopes is essential for building scalable and efficient NestJS applications, especially when managing state or resources per request or per injection.

💼 Career

Many backend developer roles using NestJS require knowledge of provider scopes to optimize performance and resource management in server-side applications.

1

Create DefaultService with default scope

Create a service class called DefaultService with a property id set to a random number using Math.random(). Use the default provider scope (no special decorator needed).

NestJS

// Create DefaultService class with an id property set to Math.random()
// Your code here

Need a hint?

Use @Injectable() without any scope option to create a default singleton service.

2

Create RequestService with request scope

Create a service class called RequestService with a property id set to Math.random(). Use @Injectable({ scope: Scope.REQUEST }) to make it request-scoped. Import Scope from @nestjs/common.

NestJS

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

@Injectable()
export class DefaultService {
  id = Math.random();
}

// Create RequestService class with request scope and id property
// Your code here

Need a hint?

Use @Injectable({ scope: Scope.REQUEST }) to create a request-scoped service.

3

Create TransientService with transient scope

Create a service class called TransientService with a property id set to Math.random(). Use @Injectable({ scope: Scope.TRANSIENT }) to make it transient-scoped. Import Scope from @nestjs/common if not already imported.

NestJS

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

@Injectable()
export class DefaultService {
  id = Math.random();
}

@Injectable({ scope: Scope.REQUEST })
export class RequestService {
  id = Math.random();
}

// Create TransientService class with transient scope and id property
// Your code here

Need a hint?

Use @Injectable({ scope: Scope.TRANSIENT }) to create a transient-scoped service.

4

Inject services into AppController and add getScopes() method

Create a controller class called AppController. Inject DefaultService, RequestService, and TransientService via the constructor. Add a method called getScopes() that returns an object with keys defaultId, requestId, and transientId holding the id values from each service instance.

NestJS

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

import { DefaultService } from './default.service';
import { RequestService } from './request.service';
import { TransientService } from './transient.service';

// Create AppController class
// Inject DefaultService, RequestService, TransientService
// Add getScopes() method returning their id values
// Your code here

Need a hint?

Inject the services in the constructor and return their id properties in getScopes().