code: function(element, valueAccessor, allBindings, viewModel, bindingContext) {
        var $element = $(element);
        var observable = valueAccessor();
  
        if (ko.unwrap(observable)) {
          $element.datepicker('update', observable.datePicker().format('DD.MM.YYYY')); // same as for .datepicker()));
        }
      }
docs: from js => to "html"