Promise objects have only the then method and maybe a few other utility methods. But using promises for chaining asynchronous operations require more complex objects. For instance, jQuery's animate method should return a promise with an animate method so you can do $(selector).animate(opts1).animate(opts2).

I see two basic approaches to this: prototypical inheritance or "parasitic" inheritance (copying properties). How have you folks been dealing with this? What have you learned so far? Would you do anything differently?