code: function modelItemMediator(item, index) {
      const { Model } = this;
  
      // if an item is already instance of Model
      if (item instanceof Model) {
          return item;
      }
  
      let itemData;
  
      if (item && typeof item.toJSON === 'function') {
          // if item is not falsy and if it has toJSON method
          // then retrieve instance data by this method
          itemData = item.toJSON(false);
      } else {
          // if not then use an item as its data
          itemData = item;
      }
  
      return new Model(itemData, this, index);
  }
docs: the function returns array item converted to Model instance