What are providers in Angular2?

Question

In the Angular2 component configuration providers is one of the keys that we could specify. How are these providers defined and what are they used for?

Answer 1

Think of providers like a recipe that tells angular how to inject a service.

We often declare providers in angular this way:

providers: [AnyService]

This is just a short hand for this:

[new Provider(AnyService, {useClass: AnyService})]

Both approaches are saying: Whenever someone requires "AnyService", provide the class "AnyService"

See that even though I'm providing the same class in the example above, in another scenario I could do something like this.

[new Provider(AnyService, {useClass: AnyServiceCustom})]

But in both scenarios, constructor would remain the same:

constructor( private _anyService: AnyService) {
}

To understand it better you need to understand how dependency injection works in Angular 2 as providers are directly related to it.

This is a must-read for every angular 2 developer.

https://angular.io/docs/ts/latest/guide/dependency-injection.html?The%20Provider%20class%20and%20provide%20function#!#injector-providers