Declare Dependency

Once you have identifiers and dependency items, you need to declare the relationships between them.

On a Class

Use the @Inject decorator on constructor parameters:


class MapService {
  constructor(
    @Inject(SatelliteService) private readonly satellite: SatelliteService
  ) {}
}

You can also use an IdentifierDecorator directly:


interface IPlatformService {}
const IPlatformService = createIdentifier<IPlatformService>("platform");
 
class DialogService {
  constructor(
    @IPlatformService private readonly platform: IPlatformService
  ) {}
}

On a Factory

List dependencies in the deps array:


const injector = new Injector([
  [I18NService],
  [
    IFormatter,
    {
      useFactory: (i18n: I18NService) => {
        return i18n.isChinese() ? new ChineseFormatter() : new EnglishFormatter();
      },
      deps: [I18NService],
    },
  ],
]);

Optional Dependencies

By default, missing dependencies throw an error. Use @Optional to allow null:


class MapService {
  constructor(
    @Optional(SatelliteService) private readonly satellite?: SatelliteService
  ) {}
}
 
const injector = new Injector([[MapService]]);
injector.get(MapService); // Works! satellite is undefined

Multiple Instances

Use @Many to inject all registered instances as an array:


class MapService {
  constructor(
    @Many(ISatelliteService) private readonly satellites: ISatelliteService[]
  ) {}
}
 
const injector = new Injector([
  [MapService],
  [ISatelliteService, { useClass: GPSSatellite }],
  [ISatelliteService, { useClass: BeidouSatellite }],
]);
 
// satellites array contains both GPS and Beidou instances