Initializing Typescript class values from constructor

Best I can come up with to allow you to have a base deserialization routine that is called from the constructor is this (modified to remove knockout dependency for testing):

class utils {
    public static CopyProperties(source:any, target:any):void {
        for(var prop in source){
            if(target[prop] !== undefined){
                target[prop] = source[prop];
            }
            else {
                console.error("Cannot set undefined property: " + prop);
            }
        }
    }
}

class Product {
  Name = "Name";

  constructor(source) {
    this.init(source);
  }

  init(source){
     utils.CopyProperties(source,this);
  }
}

class Inventory extends Product {
  Quantity;
  Price;

  constructor(source) {
    super(source);
  }

  init(source){
      this.Quantity = 0;
      this.Price = 0;
      super.init(source);
  }
}

var item = new Inventory({ Name: "Test", Quantity: 1, Price: 100 });

It is odd that the variables are only initialized in the JS after the call to super(). Maybe worth raising a work item on codeplex?

Playground.

This approach seems to work for me:

/// <reference path="knockout.d.ts" />

export class Product {
    Name: KnockoutObservableString;

    constructor(source) {
        this.Name = ko.observable(source.Name);
    }
}

export class Inventory extends Product {
    Quantity: KnockoutObservableNumber;
    Price: KnockoutObservableNumber;

    constructor(source) {
        super(source);
        this.Quantity = ko.observable(source.Quantity);
        this.Price = ko.observable(source.Price);
    }
}

var item = new Inventory({ Name: "Test", Quantity: 1, Price: 100 });