How to use the @covalent/core.TdDataTableSortingOrder.Descending function in @covalent/core

toggleRow: (any) => Observable;
  @Input()
  addRow: () => Observable;
  @Input()
  dateFilter: any = null;

  shops: RetailShop[] = [];
  shop: RetailShop;
  shopsSub: Subscription;
  shopSub: Subscription;
  currentPage: number = 1;
  pageSize: number = 50;
  sortBy: string = 'id';
  fromDate: Date;
  toDate: Date;
  sortOrder: TdDataTableSortingOrder = TdDataTableSortingOrder.Descending;

  constructor(private _loadingService: TdLoadingService,
              private _shopService: RetailShopsService) {
    this._loadingService.create({
      name: 'tables',
      type: LoadingType.Circular,
      mode: LoadingMode.Indeterminate,
      color: 'warn',
    });
  }

  ngOnInit() {
    this.shop = this._shopService.shop;
    this.shops = this._shopService.shops;
    this.getData();
    this.shopsSub = this._shopService.shops$.subscribe((data: RetailShop[]) => {

sort(name: string, sortOrder: TdDataTableSortingOrder): void {
    this.sortBy = name;
    if (sortOrder.toString() == 'ASC') {
      this.sortOrder = TdDataTableSortingOrder.Descending
    }
    else {
      this.sortOrder = TdDataTableSortingOrder.Ascending
    }
    this.filter();
  }

sort(name: string, sortOrder: TdDataTableSortingOrder): void {
    this.sortBy = name;
    if (sortOrder.toString() == 'ASC') {
      this.sortOrder = TdDataTableSortingOrder.Descending
    }
    else {
      this.sortOrder = TdDataTableSortingOrder.Ascending
    }
    this.getData();
  }

sort(name: string, sortOrder: TdDataTableSortingOrder): void {
    this.sortBy = name;
    if (sortOrder.toString() == 'ASC') {
      this.sortOrder = TdDataTableSortingOrder.Descending
    }
    else {
      this.sortOrder = TdDataTableSortingOrder.Ascending
    }
    this.getData();
  }
  search(searchTerm: string): void {