The Services module

Services are also singletons, like resources, so follow the same steps as the resources module:

1. Open the services/ProductService.js file.

2. Create the top hierarchy module:

   var Shop;
   Shop = Shop || {};

3. Create the Resources namespace:

   Shop.Services = Shop.Services || {};

4. Define ProductService:

   Shop.Services.ProductService = (function(){
   })();

5. In this case the service has no dependencies.

6. Finally, set the following code in the services/ProductService.js file. Since in the application the resources are singleton, extend the resource with the methods used in the following code:

   var Shop;
   Shop = Shop || {};
   Shop.Services = Shop.Services || {};
   Shop.Services.ProductService = (function(Product) {
     var hasStock = function (product) {
       return product.stock() > 0;
     };
   
     var decreaseStock = function (product) {
       var s = product.stock();
       if (s > 0) {
         s--;
       }
       product.stock(s);
     };
   
     var clone = function (product) {
       return Product(product.id(), product.name...