Dynamics CRM JavaScript Set Field Visible

function TickerChange() {
   if(Xrm.Page.getAttribute("tickersymbol").getValue() == null) {
       Xrm.Page.getControl("fax").setVisible(false);
   }
   else {
       Xrm.Page.getControl("fax").setVisible(true);
   }
}
Relieved Ratel