ExistingProvider

Stable Interface

What it does

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

How to use

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

Interface Overview

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

Interface Description

For more details, see the Dependency Injection Guide.

Example

class Greeting {
  salutation = 'Hello';
}

class FormalGreeting extends Greeting {
  salutation = 'Greetings';
}

const injector = ReflectiveInjector.resolveAndCreate(
    [FormalGreeting, {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));

Interface Details

provide : any

An injection token. (Typically an instance of Type or OpaqueToken, 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.

const injector = ReflectiveInjector.resolveAndCreate([
  {provide: 'local', multi: true, useValue: 'en'},
  {provide: 'local', multi: true, useValue: 'sk'},
]);

const locales: string[] = injector.get('local');
expect(locales).toEqual(['en', 'sk']);

exported from @angular/core/index, defined in @angular/core/src/di/provider.ts