Question

I am trying to use JavaScript to validate that the date selected is not earlier than today, but when I select today’s date it’s showing the alert box.

JavaScript:

function checkDueDate(sender, args) {
    var td = new Date(); 
    td.setMinutes(59);
    td.setSeconds(59);
    td.setHours(23);
    //to move back one day
    td.setDate(td.getDate() - 1);

    if (sender._selectedDate < td) {
        alert("You can't select day from the past! " + td + "");
        sender._selectedDate = new Date();
        // set the date back to the current date
        sender._textbox.set_Value(sender._selectedDate.format(sender._format))
    }

ASP.NET:

        <asp:TextBox ID="txtDueDate" runat="server"></asp:TextBox>
        <asp:CalendarExtender ID="txtDueDate_CalendarExtender" runat="server" 
            TargetControlID="txtDueDate" OnClientDateSelectionChanged="checkDueDate">
        </asp:CalendarExtender>

Answer 1

I think maybe you’re complicating things too much. I would just subtract a day in miliseconds and it should work:

function isPast( date ) {
  return date.getTime() < (new Date().getTime() - 864e5); 
}

Demo: http://jsbin.com/igeyov/1/edit