retrieve date format from database in a textbox using JQuery

yeah I have updated but now the value of textbox is "invalid date".

This is my webmethod code from c#:

public static string GetReservationById(int Id)
{
ReservationInfo _ReservationInfo = new ReservationInfo();
_ReservationInfo.ReservationId = Id;
var result = new
{
reservationInfo = _ReservationInfo.GetReservationById(),

};
var serializer = new JavaScriptSerializer();
return serializer.Serialize(result);
}
#endregion


and this the code inside the GetReservationById() method:

public IEnumerable<reservationinfo> GetReservationById()
{
using (SqlDataReader reader = SqlHelper.ExecuteReader(SqlHelper.GetConnection(), "[GetReservationById]", ReservationId))
{
if (reader.HasRows)
{
while (reader.Read())
{
yield return new ReservationInfo
{
Checkin = Convert.ToDateTime(reader["Checkin"]),
Checkout = Convert.ToDateTime(reader["Checkout"]),
};
}
}
}

}
and this my sp:

ALTER proc [dbo].[GetReservationById]
@ReservationId int
as
begin
select RS.ReservationId,convert(nvarchar(50),RS.Checkin, 101) as Checkin, convert(nvarchar(50),RS.Checkout, 101) Checkout,RS.IsReservedOn, RS.IsModifiedOn,
C.CustomerFirstName, C.CustomerSecondName, C.CustomerEmail, C.CustomerTelephone,
C.CustomerAddressLine1, C.CustomerPOB, C.City, C.Country, R.RoomName,
R.RoomPrice, R.RoomDescription, R.RoomNbrPlace, R.IsAvailable, RT.ReservationType
from Reservation RS
inner join Customer C on C.CustomerId = RS.CustomerId
inner join Room R on R.RoomId = RS.RoomId
inner join ReservationType RT on RT.ReservationTypeID = RS.ReservationTypeId
Where RS.ReservationId = @ReservationId --and R.IsAvailable = 0

end

and this my Jquery code:

function BtnEdit() {

$('a.item-edit').on("click", function (e) {
e.preventDefault();
var $editedtr = $(this).closest("tr").get(0);
showloading();
var aData = $itemTable.fnGetData($editedtr);
$Id = aData[index];
PageMethods.GetReservationById(aData[index], function (response) {
var result = eval("(" + response + ")");
if ($('#<%=txtRoomName.ClientID%>').length > 0) {
$("#<%=txtCheckin.ClientID%>").val(new Date(result.reservationInfo[0].Checkin).toString());
$("#<%=txtCheckout.ClientID%>").val(new Date(result.reservationInfo[0].Checkout));
$("#<%=txtRoomName.ClientID%>").val(result.reservationInfo[0].RoomName);
$("#<%=txtRoomDescription.ClientID%>").val(result.reservationInfo[0].RoomDescription);
$('#ddlRoomType').val();
$('#ddlNbrePlace').val();
if (result.reservationInfo[0].IsDisplayed)
$('#<%=chkbTax.ClientID%>').trigger("click");
}
$('#pnlGrid').hide();
$('#pnlEntry').show();
hideloading();
});
});
}