Very odd event behaviour for onChange on Telerik MVC DatePicker - asp.net-mvc

Question

To the question started, my code (I'll try to only include relevant portions to start), starting with my script:
function RaceDate_onChange() {
var pickedDate = $(this).data('tDatePicker').value();
var month = pickedDate.getMonth() + 1;
$.get("/RaceCard/Details?year=" + pickedDate.getFullYear() + "&month=" + month + "&day=" + pickedDate.getDate());
}
Then my markup:
#Html.Telerik().DatePickerFor(model => model.RaceDate).ClientEvents(events => events.OnChange("RaceDate_onChange"))
And finally a bit of the receiving action:
[HttpGet]
public ActionResult Details(int year, int month, int day)
{
var viewModel = new RaceCardModel {Metadata = DetailModelMetadata.Display, RaceDate = new DateTime(year, month, day)};
I'm trying to get the selection of a new date to trigger a GET, to refresh the page without submitting a form. This works fine, except for this problem:
In GET requests to the Details action, the day value is always one day behind the DatePicker. E.g. The first value is set from a view model property, when the view is rendered, say 3. I then click on 14 and hit my breakpoint in the action method. The day value is 3. When I click on 29 and hit the breakpoint, the day value is 14.
Besides asking what is wrong, I'll take a liberty and ask if there is a better way that is no more complicated. I am fairly novice and would rather deliver working code that needs revision than get bogged down in tangents and details.

Answer 1

Try using e.value instead as shown in the client-side events example. You are probably using an older version where the value() method returned the previous value during the OnChange event.
UPDATE:
"e.value" means the value field of the OnChange arguments:
function onChange(e) {
var date = e.value; // instead of datePicker.value()
}

Answer 2

As far as the 1 month difference you are getting, that's normal, and it is how the getMonth() method works in javascript on a Date instance:
The value returned by getMonth is an
integer between 0 and 11. 0
corresponds to January, 1 to February,
and so on.
So adding +1 is the correct way to cope with the situation, exactly as you did.
Just a little remark about your AJAX call: never hardcode urls. Always use url helpers when dealing with urls:
var year = pickedDate.getFullYear();
var month = pickedDate.getMonth() + 1;
var day = pickedDate.getDate();
var url = '#Url.Action("Details", "RaceCard")';
$.get(url, { year: year, month: month, day: day }, function(result) {
// process the results of the AJAX call
});