Preventing user to select date greater than today in Ajax calender extender.

<script type="text/javascript">

function checkDate(sender, args) {
            if (sender._selectedDate > new Date()) {
                alert("You cannot select a day Greater than today!");
                sender._selectedDate = new Date();
                // set the date back to the current date
                sender._textbox.set_Value(sender._selectedDate.format(sender._format))
            }

</script>


Design:


  <asp:TextBox ID="txt_FDate" runat="server" Width="100px"></asp:TextBox>
                <img id="calendar_Img1" src="Images/calendar.gif" alt="Calendar" />
                <cc1:CalendarExtender ID="CalendarExtender1" runat="server" TargetControlID="txt_FDate"
                    CssClass="cal_Theme1" Format="yyyy-MM-dd" PopupButtonID="calendar_Img1" OnClientDateSelectionChanged="checkDate">
                </cc1:CalendarExtender>