<div id="cstpodiv">
   <label>Customer PO Number <b style="color:red;">*</b></label><input name="ponum" id="cstpofield" class="inputvalues" placeholder="Enter PO number..." required/><br>
</div>

<div id="por">
   <label>PO Recieved <b style="color:red;">*</b></label> <input name="porecieved" type="date" class="input values " id="porval" onchange="blah()" placeholder="Enter date recieved..." required/><br>
  <label>PO End Date</label> <input name="poend" type="date" id="poeval" class="inputvalues " readonly/><br>
</div>

$('#status').change(function(){
          var st = $(this).val();
          var cstpofield = $('#cstpofield');
          var hidden1 = $('#cstpodiv');
          var hidden2 = $('#por');
          var por = $('#porval');

           if(st == 1){ //if status is pending
             cstpo.removeAttr('requried');
             cstpo.val('');
             hidden1.hide('slow');

             por.prop('requried', false);
             por.val('');
             hidden2.hide('slow');
           }else{
             hidden1.show('slow');
             cstpo.prop("requried", true);

             hidden2.show('slow');
             por.prop("requried", true);
           }
          });