Create Purchase Order from Sales Order

I am trying to create a purchase order from the custom fields in sales order by just one click. and a new window showing the purchase order information is shown afterward.

I have created a User Event script for creating the button and a Client Script to create the record.

The User Event script:

function onClick(type,form)  {     form.addButton('custpage_Add','Create PO',"createPO();");     form.setScript('customscriptcscreatepo');    }

The Client Script

function createPO()  {   var recId = request.getParameter('id');      var recSO = nlapiLoadRecord('salesorder',recId);      //create PO   var recPO = nlapiCreateRecord('purchaseorder');   var recPOId = recPO.getId();      var vendor = recSO.getFieldValue('custbodyfactoryname');   recPO.setFieldValue('entity',vendor);     var itemname = recSO.getFieldValue('custbodyitem');   var unitprice = recSO.getFieldValue('custbodyunitcost');   var POTotal = recSO.getFieldValue('custbodytotalfactorycost');   recPO.selectNewLineItem('item');   recPO.setCurrentLineItemValue('item', 'item', itemname);   recPO.setCurrentLineItemValue('item', 'rate', unitprice);   recPO.setCurrentLineItemValue('item', 'amount', POtotal);   recPO.commitLineItem('item');       var reqPOId = nlapiSubmitRecord(recPO, false, true);   var POURL = nlapiResolveURL('RECORD', 'purchaseorder', recPOId, true);   window.open(POURL, '_blank');  }