This site uses cookies from Google to deliver its services and to analyze traffic.
Learn more
Skip to main content
Say hello to Angular's future home!Check out Angular.devHome
/
API > @angular/core

ExistingProvider

Configures the Injector to return a value of another useExisting token.

      
      interface ExistingProvider extends ExistingSansProvider {
  provide: any
  multi?: boolean

  // inherited from core/ExistingSansProvider
  useExisting: any
}

See also

Properties

Property Description
provide: any

An injection token. Typically an instance of Type or InjectionToken, but can be any.
multi?: boolean

When true, injector returns an array of instances. This is useful to allow multiple providers spread across many files to provide configuration information to a common token.

Usage notes

      
      class Greeting {
  salutation = 'Hello';
}

class FormalGreeting extends Greeting {
  override salutation = 'Greetings';
}

const injector = Injector.create({
  providers: [
    {provide: FormalGreeting, deps: []},
    {provide: Greeting, useExisting: FormalGreeting},
  ],
});

expect(injector.get(Greeting).salutation).toEqual('Greetings');
expect(injector.get(FormalGreeting).salutation).toEqual('Greetings');
expect(injector.get(FormalGreeting)).toBe(injector.get(Greeting));

Multi-value example

      
      const locale = new InjectionToken<string[]>('locale');
const injector = Injector.create({
  providers: [
    {provide: locale, multi: true, useValue: 'en'},
    {provide: locale, multi: true, useValue: 'sk'},
  ],
});

const locales: string[] = injector.get(locale);
expect(locales).toEqual(['en', 'sk']);