Typescript scopes event 'zoom_changed' a funcionar

declare var google: any;

@IonicPage()
@Component({
  selector: 'page-photo-on',
  templateUrl: 'photo-on.html'
})
export class PhotoOnPage {
  public zoomOk: boolean;
  
  constructor(...){
    ...
  }

  setZoomState(v: boolean = false) {
    this.zoomOk = v; 
  }


public loadMap(){
    google
      .maps
      .event
      .addListener(this.map, 'zoom_changed',
        () => {
          let zoom = this.map.getZoom();
          if (zoom <= 11 && !this.showOneTime ){ 
            this.presentToast('To view spots please zoom in.');
          } 
          
          this.setZoomState((zoom >= 11));
        });
}
}