What do you know about injector?

by

An injector is referred to as a service locator. It is used to receive object instances as defined by the providers, invoke methods, instantiate types, and load modules. Each Angular application consists of a single injector which helps to look upon an instance by its name.

In AngularJS, the injector is a core component of the framework that is responsible for dependency injection. Dependency injection is a design pattern that helps manage the dependencies of components in a modular and flexible way. The injector in AngularJS is responsible for creating and managing instances of objects (services, controllers, filters, etc.) and injecting them into other components when they are needed.

Key points about the injector in AngularJS:

  1. Dependency Injection (DI): AngularJS uses dependency injection to provide components with their dependencies instead of having the components create or find dependencies themselves. This promotes modularity and makes testing easier.
  2. $injector Service: In AngularJS, the $injector is the service responsible for handling dependency injection. It is the central point for interacting with the injector.
    javascript
    angular.module(‘myModule’, [])
    .controller(‘MyController’, [‘$scope’, ‘$http’, function($scope, $http) {
    // Controller logic here
    }]);

    In the example above, the array ['$scope', '$http', function($scope, $http) is a way of explicitly declaring dependencies for the controller. This is crucial for minification of code.

  3. Provider: Providers are a special type of service in AngularJS that can be configured during the configuration phase of the application. Providers are used by AngularJS internally to implement services, and the injector uses them to create instances of services.
  4. Config and Run Blocks: The $injector is used in the config and run blocks of an AngularJS application. Config blocks are executed during the configuration phase, and run blocks are executed after the injector is created and the application is bootstrapped.
    javascript
    angular.module(‘myApp’, [])
    .config([‘$provide’, function($provide) {
    // Config block logic
    }])
    .run([‘$rootScope’, function($rootScope) {
    // Run block logic
    }]);
  5. Manual Injection: You can manually inject dependencies using the $injector service if needed.
    javascript
    angular.module(‘myModule’, [])
    .controller(‘MyController’, function($injector) {
    var $http = $injector.get(‘$http’);
    // Controller logic here
    });

Understanding the role of the injector is crucial for building maintainable, testable, and modular AngularJS applications. It helps manage the flow of dependencies between different components of an application. Keep in mind that AngularJS is an older framework, and if you’re starting a new project, you might want to consider using Angular (Angular 2 and above) or other modern frameworks