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ExistingProvider

interface

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 {
  salutation = 'Greetings';
}

const injector = Injector.create([
  {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([
  {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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Licensed under the Creative Commons Attribution License 4.0.
https://angular.io/api/core/ExistingProvider