code: function(params) {
      const order = this;
  
      if (!params) {
          params = {};
      }
  
      // the standards attributes
      this.id = params.id;
      this.dateCreated = params.dateCreated;
      this.lastUpdated = params.lastUpdated;
      this.version = params.version;
  
      this.customer = params.customer;
      this.orderDate = params.orderDate;
      this.total = params.total;
  
      this.items = params.items;
  
      this.calcTotal = function() {
          order.total = 0;
  
          order.items.forEach(function(item) {
              order.total += item.price;
          });
  
          return order.total;
      };
  }
docs: define the Order and Order Item objects