@angular/core

ExistingProvider

interface

stable

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

API

    
      interface ExistingProvider extends ExistingSansProvider {}

provide

any

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

multi

boolean | undefined

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.

useExisting

any

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']);