The logical simplicity of the rules makes it impossible to resist implementation, it seems :) I love being able to draw on your version - I missed out on implem

The logical simplicity of the rules makes it impossible to resist implementation, it seems :) I love being able to draw on your version - I missed out on implementing drag events. I notice that you separate your "views" (this.cells) from your "models" (this.grid). This seems like a good idea from an MVC perspective, but I would worry that I'm forgetting to keep them in-sync in all cases.