I've done Python and C apps using Gtk+ and GNOME APIs, and now I see there's support for JavaScript in GNOME 3 thanks to GJS (and I've also heard about seed).
So, I have to ask: does it worth it? I just want to know if GJS has gained attention and is not going to be deprecated in the future.
gjs is used as the foundation for gnome-shell in GNOME 3 and for GNOME Shell Extensions so it is very unlikely to go away or get deprecated, and in fact is seeing constant improvements all the time so I can't see any reason not to use it if it suits your purpose.