Including extension assets with sprockets

I want to use middleman-sprockets to add a JS file from my extension to an existing project. I don’t know how do I have to store my JS file (rails gems are using the vendor/assets/javascripts dir but I don’t know if it’s the same for middleman) and how sprockets will recognize it, it seems to look only in the project javascripts’ directory (source/javascripts).

So I want to add my gem and require a JS’gem file with sprockets like //= require myJSFileInMyGem in my application.

I’ve just found it. I should insert my JS file in vendor/assets/javascripts, exactly the same way as Rails.