safaribook-knockout-essentials/ko-cart/js/models/product.js

var Product = function (id, name, price, stock) {
  "use strict";
  var _id = id,
    _name = name,
    _price = price,
    _stock = stock;
  return {
    id: _id,
    name: _name,
    price: _price,
    stock: _stock,
  };
};