code: function (indexMap, loadOrder) {
                  // In older versions indexMap was an object instead of a sparse array
                  if (!('length' in indexMap)) {
                      var indexArray = [],
                          index;
                      
                      for (index in indexMap) {
                          if (!isNaN(+index)) {
                              indexArray[+index] = indexMap[index];
                          }
                      }
                      
                      indexMap = indexArray;
                  }
                  
                  return Request.prototype.getPathsFromIndexes(indexMap, loadOrder);
              }
docs: this is a helper function used by Ext.Loader to flush out
  'uses' arrays for classes in some Ext versions