Providers and dependency injection are one of the most critical and unique features of Angular. They allow you to organize your code in ways that may not come intuitively at first, but provide a level maintainability that can’t be found in other web development frameworks.
Providers are classes that create and manage service objects the first time that Angular needs to resolve a dependency. Providers is used to register the classes to an angular module as a service. And then, this service classes can be used by other components during the itself creation phase in the module.
Also Know, what is useFactory in angular? The useFactory field tells Angular that the provider is a factory function whose implementation is heroServiceFactory . The deps property is an array of provider tokens.
Considering this, what is @injectable angular?
The @Injectable() decorator marks it as a service that can be injected, but Angular can’t actually inject it anywhere until you configure an Angular dependency injector with a provider of that service. The injector is responsible for creating service instances and injecting them into classes like HeroListComponent .
What is useClass in angular?
Angular creates factory for providers that will be used to instantiate provider. So for useClass angular resolves dependency from parameters array and then calls constructor with parameters while for useExisting angular gets existing resolved instance and returns it.
What are angular providers?
A provider is an object declared to Angular so that it can be injected in the constructor of your components, directives and other classes instantiated by Angular. A service is a particular type of provider that is declared with its class name, as you can see in the Angular tutorial.
What is service in angular?
Angular services are singleton objects which get instantiated only once during the lifetime of an application. The main objective of a service is to organize and share business logic, models, or data and functions with different components of an Angular application.
What is decorator in angular?
Decorators are a design pattern that is used to separate modification or decoration of a class without modifying the original source code. In AngularJS, decorators are functions that allow a service, directive or filter to be modified prior to its usage.
What is module in angular?
In Angular, a module is a mechanism to group components, directives, pipes and services that are related, in such a way that can be combined with other modules to create an application. An Angular application can be thought of as a puzzle where each piece (or each module) is needed to be able to see the full picture.
What are directives in angular?
Directives are markers on a DOM element that tell AngularJS to attach a specified behavior to that DOM element or even transform the DOM element and its children. In short, it extends the HTML. Most of the directives in AngularJS are starting with ng- where ng stands for Angular.
What is tree Shakable in angular?
Tree Shakeable Providers are a way to define services and other things to be used by Angular’s dependency injection system in a way that can improve the performance of an Angular application. By using tree shaking, we can make sure our application only includes the code that is needed for our application to run.
What is multi in provider angular?
Multi Providers in Angular. The new dependency injection system in Angular comes with a feature called “Multi Providers” that basically enable us, the consumer of the platform, to hook into certain operations and plug in custom functionality we might need in our application use case.
What is singleton service in angular?
A singleton is a class that allows only a single instance of itself to be created and gives access to that created instance. It is used in scenarios when a user wants to restrict instantiation of a class to only one object. A singleton service is a service instance that is shared across components.
What is lazy loading in angular?
What is difference between @inject and @injectable?
2 Answers. The @Injectable decorator aims to actually set some metadata about which dependencies to inject into the constructor of the associated class. The @Inject decorator must be used at the level of constructor parameters to specify metadata regarding elements to inject.
Why injectable is used in angular?
@Injectable() lets Angular know that a class can be used with the dependency injector. @Injectable() is not strictly required if the class has other Angular decorators on it or does not have any dependencies. What is important is that any class that is going to be injected with Angular is decorated.
What does injectable mean?
injectable – Medical Definition Capable of being injected: an injectable drug. n. A drug or medicine that can be injected.
What is injectable?
The injectable is a modern, temporary and highly effective method of family planning. It is injected into the upper arm or buttocks of the woman to prevent pregnancy. The injectable prevents the meeting of the egg of the woman and the sperm of the man. It works by preventing the release of a mature egg from the ovary.
What is EventEmitter in angular?
EventEmitter is an angular2 abstraction and its only purpose is to emit events in components. Quoting a comment from Rob Wormald.  EventEmitter is really an Angular abstraction, and should be used pretty much only for emitting custom Events in components.