docs: function map(dependentKey, callback) {
        var options = {
          addedItem: function(array, item, changeMeta, instanceMeta) {
            var mapped = callback.call(this, item, changeMeta.index);
            array.insertAt(changeMeta.index, mapped);
            return array;
          },
          removedItem: function(array, item, changeMeta, instanceMeta) {
            array.removeAt(changeMeta.index, 1);
            return array;
          }
        };
  
        return arrayComputed(dependentKey, options);
      }