QueryString in Javascript

///page.querystring[]
<script language=javascript>
function querystring(fieldname)
 {  
      var urlstring = document.location.search;
      if(urlstring != null)
      {
           var typequ = fieldname+"=";
           var urlend = urlstring.indexof(typequ);
           if(urlend != -1)
           {
                var paramsurl = urlstring.substring(urlend+typequ.length);
                var isend =  paramsurl.indexof('&');
                if(isend != -1)
                {
                     return paramsurl.substring(0, isend);
                }
                else
                {
                    return paramsurl;
                }
           }
           else 
           return null;
      }
     else
     return null;
 }
</script>