What is the reason behind needing to include @Injectable when performing Dependency Injection with http, but not requiring it when implementing DI with a custom service?
Illustratively:
//no @Injectable() needed in this case
export class Test {
constructor(private customService: CustomService){}
}
/*-------------*/
@Injectable() // <== must be included here
export class HttpTest {
constructor(private http: Http){}
}
When you have a parameter in the constructor that needs to be injected, it is necessary to use @Injectable(). For more information, refer to the documentation on Why @Injectable().
@Injectable()signifies that a class can be instantiated by an injector. Without this annotation, the injector will throw an error if it attempts to instantiate a class that does not have@Injectable()marked.In the initial version of
HeroService, you could have left out@Injectable()since there were no injected parameters. However, now that the service has a dependency that needs to be injected, it is essential to include it. This is because Angular mandates constructor parameter metadata for injecting aLogger.
The Test class in your example will not function without @Injectable() being added to it.
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