Disable past date in AJAX CalendarExtender in ASP.Net

i am using ajax calendar extender to display the calendar. by using javascript i filter the previous date selection. its doing the process but displaying the previous date. now i want to hide yesterday dates from my control

in my control, i m not getting startdate and enddate property.

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

 i want to hide previous dates and month from calendar. its should be active from current date only