My idea :
If there are non cancelled orders in the baskets, create a js popup alert
    

You can't create a JavaScript-only alert with three buttons. This does
not exist.

I see a couple of choices:

1. Handle the operation without JavaScript and use a <div
class="dialog alert"> in the body of the page to offer the choice of
actions. Of course this would involve a trip to the server and a page
reload.
  

2. Use a Bootstrap modal:
http://getbootstrap.com/2.3.2/javascript.html#modals An example of
this can be found in acqui/basket.tt.

Option 2 is probably most like what you're imagining.

  -- Owen

  

Mathieu Saby
Service d'Informatique Documentaire
Service Commun de la Documentation
Université Rennes 2
Téléphone : 02 99 14 12 65
Courriel : mathieu.saby@univ-rennes2.fr