Well, the code cannot infer what the 'parent' is by itself, but you can tell it. I am not sure that I understand how you want your objects to collaborate, but here's an example.
function Pizza() {
}
Pizza.prototype = {
Pizza: constructor,
newSlice: function () { return new PizzaSlice(this); },
addPepperoni: function () { console.log('add pep..'); }
};
function PizzaSlice(pizza) {
this.pizza = pizza;
//you can call pizza.whateverYouWant();
}
var pizza = new Pizza(),
pizzSlice = pizza.newSlice();