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GeezerVison is showing angular.dev — ExistingProvider • Angular

API

    
      interface ExistingProvider extends ExistingSansProvider {}

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

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.

Existing token to return. (Equivalent to injector.get(useExisting))

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']);

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