Provider scope (default, request, transient) in NestJS

Introduction

Provider scope controls how NestJS creates and shares service instances. It helps manage when and how often a service is created.

When you want a single shared service instance for the whole app (default scope).

When you need a new service instance for each incoming request (request scope).

When you want a new service instance every time it is injected (transient scope).

Syntax

NestJS

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

@Injectable({ scope: Scope.DEFAULT })
export class MyService {}

Use Scope.DEFAULT for a singleton service shared app-wide.

Use Scope.REQUEST to create a new instance per HTTP request.

Examples

This service uses the default singleton scope.

NestJS

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

@Injectable()
export class DefaultService {}

This service creates a new instance for each request.

NestJS

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

@Injectable({ scope: Scope.REQUEST })
export class RequestService {}

This service creates a new instance every time it is injected.

NestJS

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

@Injectable({ scope: Scope.TRANSIENT })
export class TransientService {}

Sample Program

This example shows a request-scoped service that generates a random ID when created. Each HTTP request gets a new service instance with a different ID.

NestJS

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

@Injectable({ scope: Scope.REQUEST })
export class RequestScopedService {
  private readonly id: number;

  constructor() {
    this.id = Math.floor(Math.random() * 1000);
  }

  getId() {
    return this.id;
  }
}

@Controller()
export class AppController {
  constructor(private readonly requestService: RequestScopedService) {}

  @Get()
  getId() {
    return `RequestScopedService ID: ${this.requestService.getId()}`;
  }
}

Important Notes

Default scope means one instance shared everywhere.

Request scope is useful for services that hold request-specific data.

Transient scope creates a fresh instance every time, useful for stateless helpers.

Summary

Provider scope controls service instance lifetime in NestJS.

Default scope shares one instance app-wide.

Request scope creates a new instance per HTTP request.

Transient scope creates a new instance every injection.