# Developer Guide: Angular Services: Understanding Angular Services

Work in Progress This page is currently being revised. It might be incomplete or contain inaccuracies.

Angular services are singletons that carry out specific tasks common to web apps, such as the `$xhr service` that provides low level access to the browser's `XMLHttpRequest` object.

To use an angular service, you identify it as a dependency for the dependent (a controller, or another service) that depends on the service. Angular's dependency injection subsystem takes care of the rest. The angular injector subsystem is in charge of service instantiation, resolution of dependencies, and provision of dependencies to factory functions as requested.

Angular injects dependencies using "constructor" injection (the service is passed in via a factory function). Because JavaScript is a dynamically typed language, angular's dependency injection subsystem cannot use static types to identify service dependencies. For this reason a dependent must explicitly define its dependencies by using the `$inject` property. For example:

        myController.$inject = ['$location'];

The angular web framework provides a set of services for common operations. Like other core angular variables and identifiers, the built-in services always start with `$` (such as `$xhr` mentioned above). You can also create your own custom services.

### Related Topics

- About Angular Dependency Injection
- Creating Angular Services
- Registering Angular Services
- Managing Service Dependencies
- Testing Angular Services

### Related API

- `Angular Service API`
- `Injector API`