function IsDate(dateStr) {

    var datePat = /^(\d{1,2})(\/|-)(\d{1,2})(\/|-)(\d{4})$/;
    var matchArray = dateStr.match(datePat); // is the format ok?

    if (matchArray == null) {
        alert("Please enter date as either mm/dd/yyyy or mm-dd-yyyy.");
        return false;
    }

    month = matchArray[1]; // p@rse date into variables
    day = matchArray[3];
    year = matchArray[5];

    if (month < 1 || month > 12) { // check month range
        alert("Month must be between 1 and 12.");
        return false;
    }

    if (day < 1 || day > 31) {
        alert("Day must be between 1 and 31.");
        return false;
    }

    if ((month == 4 || month == 6 || month == 9 || month == 11) && day == 31) {
        alert("Month " + month + " doesn`t have 31 days!");
        return false;
    }

    if (month == 2) { // check for february 29th
        var isleap = (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));
        if (day > 29 || (day == 29 && !isleap)) {
            alert("February " + year + " doesn`t have " + day + " days!");
            return false;
        }
    }
    return true; // date is valid
}

function DateDifference(strDate1, strDate2) {
    datDate1 = Date.parse(strDate1);
    datDate2 = Date.parse(strDate2);
    return (datDate2 - datDate1) / (24 * 60 * 60 * 1000)
}