add this function to your project;

function copyPrototype(descendant, parent) {
  var sConstructor = parent.toString();
  var aMatch = sConstructor.match( /\s*function (.*)\(/ );
  if ( aMatch != null ) { descendant.prototype[aMatch[1]] = parent; }
  for (var m in parent.prototype) {
    descendant.prototype[m] = parent.prototype[m];
  }
};

Then define your classes (prototypes) like so;

function AClass(param) {
   this.Text=param;
}
AClass.prototype.Speak = function() {
  alert(this.Text);
}

function BClass(param, name) {
  this.AClass(param);
  this.Name = name;
}
copyPrototype(BClass, AClass);
BClass.prototype.Speak = function() {
  alert('Hi ' + name);

  // Call overridden parent method...
  AClass.prototype.Speak.apply(this);
}

So the above example will give you 2 classes- B is derived from A.  Calling AClass.Speak will give you a single alert with the contents of the ‘text’ property, whereas BClass.Speak will give you two text boxes; the first greeting you by name, and the second being the alert box from AClass.  I’ve tested this myself with multiple generations of inheritance and it worked fine, where other methods have not.

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We wanted to create a central project containing the basket functionality which we could drop into any project and use.  So the basket needs to be able to add lots of different types of books- some from the CDS entity library or some any other entity library we use.  To do this we created an Interfaces project which holds an interface called IBook which held the minimum data required by the basket such as Title, Price, ISBN, Cover Image.  This project is then referenced by the sites, the entity libraries (like CDS or any other’s we build) and the basket itself.

Adding the book to the basket was fine, however the problem arose when viewing items- the basket needed to be able to load the book data back- this is fine we thought- we would simply add a load() method to IBook, however this didnt solve the problem as the basket only had IBook signature of load- it didn’t know which concrete implementation of load to run.

The answer was to use generics.  We added a generic parameter to the top of the basket which accepted a type which it assumed to be derived from IBook and always have a default constructor, like so;

public class Basket<T> where T : Hachette.ProcessLayer.IBook, new() {
   private List<BasketItem<T>> _basket_items;
   ...
}

Likewise we made the basket item’s generic, and pass the type T from the basket to the basket item when instanciating them- the basket items are then able to define a real book instance of type T so it knows which concrete book it’s dealing with, so it can call the correct load method. The use of generics here means the basket object can reference a real book class from the CDS project (in a separate assembly) without having to reference that assembly, meaning we can drop in any type of book from any assembly for future sites, and with the parent website stating the type to use when creating the basket, the basket can remain completely independent.

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