code: function(k) {
        var $combo = this['$'+k];
        if (!$combo) {
          return;
        }
  
        // define method name to fill items, e.g `fillDays`
        var f = 'fill' + k.charAt(0).toUpperCase() + k.slice(1); 
        var items = this[f]();
        var value = $combo.val();
  
        $combo.html('');
        for(var i=0; i<items.length; i++) {
          $combo.append('<option value="'+items[i][0]+'">'+items[i][1]+'</option>');
        }
  
        $combo.val(value);
      }
docs: /*
  Fill combo with items