FactoryProvider - Angular

Configures the Injector to return a value by invoking a useFactory function.

API

interface FactoryProvider extends FactorySansProvider {
  provide: any;
  multi?: boolean | undefined;
  override useFactory: Function;
  override deps?: any[] | undefined;
}

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.

useFactory

Function

A function to invoke to create a value for this token. The function is invoked with resolved values of tokens in the deps field.

deps

any[] | undefined

A list of tokens to be resolved by the injector. The list of values is then used as arguments to the useFactory function.

Usage Notes

const Location = new InjectionToken('location');
        const Hash = new InjectionToken('hash');

        const injector = Injector.create({
          providers: [
            {provide: Location, useValue: 'https://angular.io/#someLocation'},
            {
              provide: Hash,
              useFactory: (location: string) => location.split('#')[1],
              deps: [Location],
            },
          ],
        });

        expect(injector.get(Hash)).toEqual('someLocation');

Dependencies can also be marked as optional:

const Location = new InjectionToken('location');
        const Hash = new InjectionToken('hash');

        const injector = Injector.create({
          providers: [
            {
              provide: Hash,
              useFactory: (location: string) => `Hash for: ${location}`,
              // use a nested array to define metadata for dependencies.
              deps: [[new Optional(), Location]],
            },
          ],
        });

        expect(injector.get(Hash)).toEqual('Hash for: null');

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']);