コード匂い114 -空のクラス

TL;DR: Remove all empty classes.

class ShopItem { 
  code() { }
  description() { }                 
}

class BookItem extends ShopItem { 
   code() { return 'book' }
   description() { return 'some book'}     
}

// concrete Class has no real behavior, just return different 'data'

class ShopItem { 
  constructor(code, description){
    //validate code and description
    this._code = code;
    this._description = description;
  }
  code() { return this._code }
  description() { return this._description }                 
  //Add more functions to avoid anemic classes
  //getters are also code smells, so we need to iterate it
}

bookItem = new ShopItem('book', 'some book);
//create more items

An error arises from treating object variables (instance variables) as if they were data attributes and then creating your hierarchy based on shared attributes. Always create hierarchies based on shared behaviors, side.