How to validate fields on item fulfilment form

Hi ,

We have two custom fields in item fulfilment line level (Start date and End date), I want to validate both the dates should not be same.

I tried below , somehow it is not giving the alert when both are same.

function validateLine()

 {

  var GetRecord = nlapiGetRecordType();

   if (GetRecord == 'itemfulfillment') {

     var startdate = nlapiGetCurrentLineItemValue('item', 'custcol_contract_start')

    var enddate = nlapiGetCurrentLineItemValue('item', 'custcol_contract_end')

       if (startdate == enddate)

      {

      alert('Contract start and end should be different');

      return false;

       }

       return true;

   }

   }

 

I thought of using workflow , But the above custom fields are not available for comparison(Actions used : Confirm, Show message. Both didn't work for me)