Date Comparison in javascript

There are two functions fromdate and todate which accept the parameter as an id of the text field.

<script type="text/javascript">
function FromDate(getID) {
                                                  
       document.getElementById('SalesEndDate').value = "";
       var dateString = document.getElementById(getID).value;
       var target = new Date(dateString);
       var now = new Date;
       
       if(now<=target)
       {
           return true;
       }
       else
       {
           alert("Starting date must be current or future date.");
                   document.getElementById(getID).value = "";
                  
                   return false;
       }
       
   }
function ToDate(getID) {
       var dateString = document.getElementById(getID).value;
       var toDate1 = new Date(dateString);
       var datestring1 = document.getElementById('SalesFromDate').value;
        var FromDate = new Date(datestring1);
        if(FromDate<=toDate1)
        {

            return true;
        }
        else
        {
           alert("End date must be Start or future date.");
                    document.getElementById(getID).value = "";
                    
                    return false;
        }

    }
</script>