Using prototype for KnockoutJS computed properties

Question

Is it recommended to create computed properties on the prototype object?

This is what I've attempted below but the firstName binding is returning the function as a string rather than executing it (http://jsfiddle.net/W37Yh).

var HomeViewModel = function(config, $, undefined) {

    if (!this instanceof HomeViewModel) {
        return new HomeViewModel(config, $, undefined);
    }

    this.firstName = ko.observable(config.firstName);
    this.lastName = ko.observable(config.lastName);
};

HomeViewModel.prototype.fullName = function() {
    return ko.computed(function() {
        return this.firstName() + " " + this.lastName();
    }, this);
};

var model = new HomeViewModel({
    firstName: "John",
    lastName: "Smith"
}, jQuery);

ko.applyBindings(model);​

Answer 1

this is not the Actual viewmodel since the instance is not created yet. You can do

ViewModel = function() {
   this.fullName = ko.computed(this.getFullName, this);
};

ViewModel.prototype = {
   getFullName: function() {
      return this.firstName() + " " + this.lastName();
   }
};