Gnome Shell JavaScript Documentation
mathematicalcoffee.blogspot.com
mathematicalcoffee.blogspot.com
Per the GNOME docs [1] it sounds like there still isn't much documentation for the GNOME Shell Javascript code.
I've been working on triplescripts.org, and I have plans to dive into Gnome and GJS, with the goal being to highlight GJS as a potential target for the system layer. Along the way, I intend to pour some energy into the Gnome/GJS docs. In the past, I was heavily involved in shaping the JS docs on developer.mozilla.org in its early days (ca 2006–2008).
For pragmatic reasons, triplescripts.org is "launching" with a focus on NodeJS right now, due to its ubiquity. GJS is a capable alternative, though, especially for environments where you'd expect it to be installed and where NodeJS isn't already, like default Ubuntu installs.