ANGULAR ASYNC

 positionChanged = new Subject();

  getLocation() {
    if ("geolocation" in navigator) {
      navigator.geolocation.watchPosition((success) => {
        this.lat = success.coords.latitude;
        this.lon = success.coords.longitude;
        this.positionChanged.next();        
      })
    }
    this.positionChanged.pipe(
       mergeMap(()=>this.todayService.daitriecoordinatebi(this.lat, this.lon)))
        .subscribe(data => {
          this.amindiDGES = data;
        })
  }