To create a gnome-shell extension I started writing GJS bindings for PureScript. I wrote enough FFI to implement simple Gtk4 applications and Clutter widgets, and it seems like the rest of the API could be generated from the GIR description. You can find the project here: purescript-gjs.
Anyway, it seems like PureScript is working really well for GJS. Please let me know if you are interested, I’d be happy to add you to the project.