@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']);