comparing dates in php application

<script language="javascript">
function datevali()
{
    //alert('hi');
    var startdate = document.getElementById('fromdate').value;
   var enddate  = document.getElementById('amce').value;
   var todate = document.getElementById('todate').value;
   var amcs = document.getElementById('amcs').value;

   var d1 = new Date(startdate)
   var d2 = new Date(enddate)
   var d3= new Date(todate)
   var d4= new Date(amcs)
   //alert(d1);
  // alert(d2);

   if (d2 < d1) {
      alert ("Disposed Date Must be graterthan Warranty Expiry Date ") ;
                }
                if (d3 > d4) {
      alert ("Commissioned date must be grater than delivered date ") ;
                }
                if (d1 < d4) {
      alert ("Warranty Expiry Date Must be graterthan Commissioned date") ;
                }
                if (d1 < d3) {
      alert ("Warranty Expiry Date Must be graterthan delivered date") ;
                }

}
</script>