Introduction to Angular Dependency Injection

Angular is a powerful front-end development framework that allows developers to create complex and dynamic web applications with ease. One of the key features that contributes to this ease of development is Angular’s dependency injection.

In this article, we will introduce the concept of dependency injection, explain how it works in Angular, and provide some common FAQs related to Angular dependency injection.

What is Dependency Injection?

Dependency injection is a programming technique in which an object receives its dependencies from an external source rather than creating them itself. In simpler terms, it’s a way of designing a system where the components are loosely coupled, which makes it easier to test and maintain.

In traditional programming, objects are responsible for creating their dependencies. This can often result in tightly coupled code that is difficult to test, refactor, and maintain. Dependency injection solves this problem by separating the creation of objects and the management of their dependencies.

In Angular, dependency injection is a built-in feature of the framework that allows you to define dependencies for your services, controllers, and other components. When Angular needs to create an instance of a component, it looks to see if any of the dependencies have been defined and if so, it injects them into the component.

How does Dependency Injection work in Angular?

When you register a service or a component with Angular, you can specify any dependencies it requires. Angular will then use its injector to provide those dependencies when the component or service is created.

For example, let’s say we have a service called `UserService` that depends on another service called `HttpClient`. In Angular, we would register `UserService` in the `providers` array of an Angular module and specify that it requires an instance of `HttpClient` like this:

import { Injectable } from ‘@angular/core’;
import { HttpClient } from ‘@angular/common/http’;

providedIn: ‘root’
export class UserService {
constructor(private http: HttpClient) {}

getUsers() {
return this.http.get(‘’);

As you can see here, we have used the `@Injectable` decorator to annotate the `UserService` class, which tells Angular that this class can have dependencies injected into it. We have also specified the `HttpClient` dependency through the constructor argument.

When Angular needs to create an instance of `UserService`, it will see that it has a dependency on `HttpClient` and check if there is a registered instance of `HttpClient`. If there is, it will inject that instance into `UserService`, otherwise, it will create a new instance of `HttpClient` and inject that.

This process of injecting dependencies can be done at any level in an Angular application. For example, components can have dependencies injected into them, which can also have their own dependencies. The entire process is handled by Angular’s injector, which manages the creation and injection of dependencies.


Q: What is the benefit of using Dependency Injection in Angular?

A: Dependency Injection in Angular makes it much easier to write maintainable, scalable, and testable code. It separates the definition of dependencies from the creation of objects, which leads to looser coupling and better code organization.

Q: Can I inject multiple dependencies into a component or service?

A: Yes, you can inject as many dependencies as you need into a component or service. Simply list them as constructor arguments, and Angular will handle the injection process.

Q: How does Angular know which service or component to inject?

A: Angular uses the `@Injectable` decorator to identify services or components that can have dependencies injected into them. When you register a service or component, you must specify the `@Injectable` decorator if you want it to support dependency injection.


Dependency injection is a powerful technique for designing maintainable and scalable code. Angular’s built-in support for Dependency Injection makes it easy to implement and use in your application. By using Dependency Injection effectively, you can write more maintainable, scalable, and testable code in Angular.

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