As they said in Github issue:
Franzliedke wrote I guess this one should still be kept open, because "only" basic infrastructure (Webpack, heh) was done so far. In contrast to #851, which I will close in favor of some smaller issues, one per missing extender type.
So they've done some part, but not finished, so issue is still there. In the roadmap it is actually written, that they want to polish JS API in the future, so it is not unexpected.
I hope they are cleaning it up, because the want to finish the beta8 job soon?
