...
import { HttpOverlayModule } from 'a4-http-overlay-interceptor';
...

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    ...,
    HttpOverlayModule,
    ...
  ],
  ...
})

constructor(private httpOverlayService: HttpOverlayService) { }

this.httpOverlayService.setOverlayCallBacks(
    () => {
        ... // show spinner code
    }, () => {
        ... // hide spinner code
    }
);