Dependency Injection (DI) is a design pattern used in software development to manage the dependencies between different components of an application. In the context of AngularJS, DI is a core feature that allows developers to easily create and manage dependencies between different parts of their application.
In AngularJS, DI is achieved by using the built-in dependency injection system provided by the framework. This system allows developers to define dependencies for their components and have them automatically injected when the component is instantiated.
To understand how DI works in AngularJS, let’s consider an example. Suppose we have a controller that needs to make HTTP requests to a server. Instead of directly creating an instance of the $http service inside the controller, we can define it as a dependency and have it injected automatically.
Here’s how we can define the controller with its dependencies:
javascript
angular.module(‘myApp’, [])
.controller(‘MyController’, [‘$http’, function($http) {
// Controller logic here
}]);
In this example, we define a controller called "MyController" and specify its dependencies using an array notation. The first element of the array is the name of the dependency (in this case, "$http"), and the second element is a function that will be called with the injected dependency.
When AngularJS instantiates the "MyController" controller, it will automatically inject an instance of the $http service into the controller’s function. This allows us to use the $http service inside the controller without having to manually create an instance of it.
The DI system in AngularJS is not limited to built-in services like $http. It can also be used to inject custom services, factories, providers, and other components defined by the developer.
By using DI, developers can easily manage the dependencies between different components of their application, making it easier to test, maintain, and extend the codebase. It also promotes loose coupling between components, as each component only needs to know about its dependencies, not how to create them.
Overall, DI is a powerful feature of AngularJS that helps improve the modularity and maintainability of applications by providing a convenient way to manage dependencies between different components.