Q:

ko.mapping.fromJS and Date objects

I've asked questions about knockout in the past but haven't had a chance to work on knockout since the last question was addressed. My latest question is specifically about the use of ko.mapping.fromJS where a Date object is involved.
When I use ko.mapping.fromJS to map an object that has a nested Date object that Date object gets translated to...I don't know what it is. 
Here is my jsfiddle: http://jsfiddle.net/L5sgW/46/
HTML:
<p> <span>Name:</span>
 <span data-bind="text: IntroData.Name"></span>

    <button id="update" data-bind="click: Update">Update!</button>
</p>

Javascipt:
var ViewModel = function (data) {
    var me = this;
    ko.mapping.fromJS(data, {}, me);

    me.Update = function () {
        alert(stuff2.IntroData.TestDate.toString('yyyy-MM-dd'));
        ko.mapping.fromJS(stuff2, {}, me);
        alert(me.IntroData.TestDate.toString('yyyy-MM-dd'));
    };

    return me;
};

var stuff = {
    IntroData: {
        Name: 'Test'
    }
};

var stuff2 = {
    IntroData: {
        TestDate: new Date('2013-09-01'),
        Name: 'Test2'
    }
};

window.viewModel = ko.mapping.fromJS(new ViewModel(stuff));
ko.applyBindings(window.viewModel);

When you click the "Update!" button "Stuff2.IntroData.TestDate" is displayed in the alert. Then the mapping occurs. When the alert for "me.IntroData.TestDate" happens it results in: "function d(){if(0

Why doesn't the date value get preserved? How do I preserve it?

A:

: )
Remember that you need the parentheses to get the property of TestDate -
http://jsfiddle.net/L5sgW/47/
alert(me.IntroData.TestDate().toString('yyyy-MM-dd'));

That was the only line I changed.

