In AngularJS, what are services and how are they used inside an application module?

Introduction / Context:
AngularJS is a JavaScript framework that promotes modular design by separating controllers, views, and shared logic. Services play a critical role in this architecture. They allow developers to encapsulate code that should be reused across controllers, directives, and other parts of the application. Interviewers often test whether candidates can explain what services are and why they matter for maintainable, testable AngularJS applications.

Given Data / Assumptions:

• The framework in question is AngularJS, the version one dot x framework.
• We are interested in the concept of services defined within AngularJS modules.
• Services are related to code reuse and shared responsibilities inside the application.

Concept / Approach:
In AngularJS, a service is typically a singleton object that is created once per injector. It is defined using patterns such as factory, service, or provider. Services are used to hold shared logic like communication with back end APIs, calculations, business rules, or state that needs to be accessed by multiple controllers. By injecting these services where needed, AngularJS simplifies dependency management and makes code easier to test and maintain.

Step-by-Step Solution:
Step 1: Recall that AngularJS promotes dependency injection and separation of concerns between controllers, views, and services. Step 2: Think about typical tasks handled by services, such as making HTTP requests or encapsulating business calculations. Step 3: Note that services are created once and shared, making them singleton objects within the lifetime of the application injector. Step 4: Scan the options for a description that mentions reusable, shared, or singleton functionality across different parts of the application. Step 5: Select the option that defines services as reusable singleton objects that provide shared functionality.

Verification / Alternative check:
To verify the answer, consider the code pattern in AngularJS: you define a service using module.service or module.factory, and then inject it into multiple controllers using dependency injection. The same instance is reused, which confirms that services are singletons providing shared features. They are not templates or low level processes, and they outlive individual function calls.

Why Other Options Are Wrong:
Option B: Describes HTML templates, which are part of the view layer, not services. Option C: Refers to operating system processes, which fall outside the scope of AngularJS running in a browser. Option D: Talks about temporary variables inside a controller function, which are not shared across the application and therefore do not match the purpose of services.

Common Pitfalls:
A common mistake is to put too much logic directly inside controllers instead of moving reusable logic into services. This leads to large, hard to test controllers. Another pitfall is confusion between factories and services in AngularJS; both produce services, but they differ in how they are defined. Focusing on the idea that services are shared, injectable, and reusable helps keep architectural decisions clean.

Final Answer:
In AngularJS, services are Reusable singleton objects that provide shared functionality such as data access and business logic.