gjs Lang.Class vs GObject.Class

[Aaron Paden <aaronbpaden gmail com>]

Hi. I've been looking at gnome shell extensions, though I have only a
passing familiarity with javascript. I see a lot of people using
Lang.Class and GObject.Class, but I can't seem to find any up-to-date
documentation talking about it. Could someone explain the difference? Is
GObject.Class only for extending GTypes? What are the differences in
implementing a GObject.Class and Lang.Class?