Creating the product service

If you look in the models/product.js file, you can see that the model contains some logic:

var hasStock = function () {
  return _product.stock() > 0;
};
var decreaseStock = function () {
  var s = _product.stock();
  if (s > 0) {
    s--;
  }
  _product.stock(s);
};

We are going to move this logic and some more to a service with the following steps:

1. Create a folder called services.

2. Inside it, create a file called ProductService.

3. Create a singleton object and add the hasStock and decreaseStock functions, as follows:

   var ProductService = (function() {
     var hasStock = function (product) {
       return product.stock() > 0;
     };
   
     var decreaseStock = function (product) {
       var s = product.stock();
       if (s > 0) {
         s--;
       }
       product.stock(s);
     };
   
     return {
       hasStock:hasStock,
       decreaseStock:decreaseStock
     };
   })();

4. Update the add-to-cart-button component:

   this.addToCart = function() {
     ...
     if (item) {
       CartProductService.addUnit(item...