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ExistingProvider

npm Package @angular/core
Module import { ExistingProvider } from '@angular/core';
Source core/src/di/provider.ts

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

Interface Overview

      
      interface ExistingProvider { 
  provide: any
  useExisting: any
  multi?: boolean
}

How To Use

      
      const provider: ExistingProvider = {provide: 'someToken', useExisting: 'someOtherToken'};

Description

For more details, see the "Dependency Injection Guide".

Example

      
      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));

Members

      
      provide: any

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

      
      useExisting: any

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

      
      multi?: boolean

If true, then 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.

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']);