Use private properties in descendants

[Condor]

Is it possible to use private properties in descendants?

I mean something like:

var MyClass = function() {
var prop = 'private';
return {
getProp: function() {
return prop;
}
}
}

var MyClass2 = function() {
MyClass2.superclass.constructor.call(this, arguments);
}

Ext.extend(MyClass2, MyClass, {
getProp: function() {
var prop = MyClass2.superclass.getProp.call(this);
return prop + 'extra';
}
});

var myClass2 = new MyClass2();
alert(myClass2.getProp());

(which doesn't work ofcourse)