The forRoot pattern for singleton services

pre-six.module.ts

import { ModuleWithProviders, NgModule } from '@angular/core';

import { MyComponent } from './my.component';
import { PreSixSingletonService } from './pre-six-singleton.service';

@NgModule({
  declarations: [
    MyComponent,
  ],
})
export class PreSixModule {
  static forRoot(): ModuleWithProviders {
    return {
      ngModule: PreSixmodule,
      providers: [
        PreSixSingletonService,
      ],
    };
  }
}