How to make column field null in jquery mvc

//To validate the date
function FutureDateValidation(Indx) {

    var ExpDateTxt = '#txtExpDate' + Indx.toString();
    var mCurDt = $('#CurDate').val();
    var ExpDate = $(ExpDateTxt).val();

   
    if (CompareDates(mCurDt, ExpDate) == false) {

        PopupMessage("Required", " The Expiry date should be greater than current date", "alert");

        //        $('#' + ExpDateTxt).tex = "";

        $('#' + ExpDateTxt).focus();
        e.stopPropagation();
        return false;

    }
    else {
        e.stopPropagation();
        return true;
    }
}