Can the object of type HttpSession called session be accessed from a function?

In a simple jsp page I have a function(see below) defined in the header of the page, and set to an onclick handle of for a button. When I press this button, I'll never see the second alert message. If I do something in the body of the page (like Session ID: <%= session.getId() %> ) I have no trouble accessing it. What newbie mistake am I making?

     function doTest()
 {
  alert('Preforming test 122333232');

      String sessionId = session.getId();

      alert('After access');

      if(sessionId == null)
      {
        alert('session id is null?');
      }

Thanks