Expand Panel Validation in JavaScript

<script type="text/javascript">

function ExpandPanel(num)
 {
         var obj = document.getElementById('ctl00_ContentPlaceHolder_ID' + num);
         if (obj.style.display != "block")
{
             document.getElementById('ctl00_ContentPlaceHolder_ ID ' + num).style.display = "block";
             document.getElementById('ctl00_ContentPlaceHolder_ ID ' + num).value = 'Expand';
         }
         else {
             document.getElementById('ctl00_ContentPlaceHolder_ ID ' + num).style.display = 'none';
             document.getElementById('ctl00_ContentPlaceHolder_ ID ' + num).value = 'Collapse';
         }

     }

 </script>