Knockout JS Model Inheritance

I have three relatively similar knockout models in my application and I would like to extend a base model to combine common properties rather than repeat myself three times. example ``` var ItemModel = function (item) { var self = this; self.order = ko.observable(item.order); self.title = ko.observable(item.title); self.price = ko.observable(item.price); self.type = ko.observable(item.type); }; var StandardItemModel = function (item, cartItemTypes) { var self = this; self.order = ko.observable(item.order); self.title = ko.observable(item.title); self.price = ko.observable(item.price); self.type = ko.observable(item.type); self.isInCart = ko.computed(function () { return cartItemTypes().indexOf(item.type) > -1; }, self); self.itemClass = ko.computed(function () { return self.isInCart() ? "icon-check" : "icon-check-empty"; }, self); }; var CustomItemModel = function (item) { var self = this; self.order = ko.observable(item.order); self.title = ko.observable(item.title); self.price = ko.observable(item.price); self.type = ko.observable(item.type); self.icon = item.icon; }; ``` I would like to use ItemModel as a base class and just add the extra properties as necessary.