What i've found out is, that all apps are written in Polymer (https://www.polymer-project.org). By the way, this is a very nice framework! I really like it and has a wonderful UI library.
I created a small test app, by copy paste an existing app and modify it. This is a good way to understand, how the infrastructure of the onion console works. I guess it's a benefit, if you take a look to the polymer framework. The hole UI is based on it and the app architecture as well.
The gpio app is a good example, how an app works and interact with services.
I hope, we will have as soon as possible a best practice for it.