Angular 2 Injectable Interface?

Question

Today I stumbled upon something that I didn\'t think would cause me trouble.

In Java and Spring, I can declare two beans that both implement a given interface, while

Answer 1

In order for a provider to be injected, it should be registered as a provider. There's no IConfigurationService provider. And it cannot be a provider, because interfaces don't exist in compiled JS code.

The common practice for interfaces that are supposed to be used as provider tokens is to be abstract classes:

abstract class ConfigurationService { ... }

@Injectable()
class WebAppConfigurationService extends ConfigurationService { ... }

...
providers: [{ provide: ConfigurationService, useClass: WebAppConfigurationService }]
...

This recipe is commonly used by Angular 2 itself, e.g. abstract NgLocalization class and concrete NgLocaleLocalization implementation.