i have dropdown named po_no with same id which is coming from ajax file

in po_no getting two values in the format of 1025*3

when i put validation on that dropdown in javascript i write this code

if(document.getElementById('po_no').value=="")
  {
 alert("Choose Purchase Order Number");
 return false;
  }

but this code does not work plz give me ideas

Originally asked by: user435704 on Stack Overflow