ASP.NET

function checkyear(source, arg) {
    var txtDOB = arg.Value;
    var birthdate = txtDOB.split("/");
    var yearvalue = parseInt(birthdate[2]);
    var MonthValue = parseInt(birthdate[0]);
    var DayValue = parseInt(birthdate[1]);
    var date = new Date();
    alert(yearvalue);
    alert(MonthValue);
    alert(DayValue);
    var CurrentYear = date.getFullYear();
    if (MonthValue < 1 || MonthValue > 12) {
        alert(MonthValue);
        source.errormessage = "Please enter a valid Date of birth";
        arg.IsValid = false;
        return;
    }
    if (DayValue < 1 || DayValue > 31 || (MonthValue == 2 && DayValue > daysInFebruary(yearvalue))) {

        alert(DayValue);
        source.errormessage = "Please enter a valid Date of birth";
        arg.IsValid = false;
        return;


    }
    if (yearvalue >= CurrentYear - 13) {

        source.errormessage = "Your age should be greater than 13.";
        arg.IsValid = false;
        return;
    }
    else if ((yearvalue <= 1900) || (yearvalue >= CurrentYear)) {
        source.errormessage = "Please enter a valid Date of birth";
        arg.IsValid = false;
        return;
    }
    else {
        arg.IsValid = true;
    }
}
function daysInFebruary(year) {
    // February has 29 days in any year evenly divisible by four,
    // EXCEPT for centurial years which are not also divisible by 400.

    return (((year % 4 == 0) && ((!(year % 100 == 0)) || (year % 400 == 0))) ? 29 : 28);
    alert(((year % 4 == 0) && ((!(year % 100 == 0)) || (year % 400 == 0))) ? 29 : 28);
}