title: Set session value in callback (Node.js, express.js)
body: <p>How to set session value in callback? Why it doesn't work?</p>
  
  <pre><code>app.get('/room/:id', function(req, res) {
      var room_id = req.param('id');
      room.getRoom(room_id, function(err, result) {
          if(result.length) {
              req.session.code_room = room_id;
          }
      }); 
      res.render('room.jade');
  });
  </code></pre>