Date Differance in Javascript

function ValidateDate() {
           var SDate = document.getElementById("ctl00_ContentPlaceHolder1_FromDate").value;
           var EDate = document.getElementById("ctl00_ContentPlaceHolder1_ToDate").value;


           var alertReason1 = 'To Date must be greater than or equal to From Date.'
           var alertReason2 = 'End Date can not be less than Current Date.';

           var endDate = new Date(EDate);
           var startDate = new Date(SDate);

           if (SDate != '' && EDate != '' && startDate > endDate) {
               alert(alertReason1);
               //document.getElementById(CtrlEDate).value = "";
               return false;
           }
           else if (SDate == '') {
               alert("Please enter Start Date");
               return false;
           }
           else if (EDate == '') {
               alert("Please enter End Date");
               return false;
           }
       }