Tips and Tricks: Allowing Global Definition of Components and Helpers in CakePHP

I am starting to create my layouts and pages. But I encountered this problem (much to my annoyance. How much errors could I take?):
Notice (8): Undefined variable: javascript [APP/views/layouts/default.ctp, line 14]
I remembered encountering this before on my localhost development. So I browsed my local files and see that I created an app_controller.php inside app/controllers/
The controller just have these codes:
class AppController extends Controller {
  var $helpers = array(Html’, Form’, Ajax’, Javascript’, Time”);
  var $components = array(Session’); 
which just enables you to allow the use of the following helpers and components all throughout your cakePHP application without redefining these on individual controllers.
so. ciao! n