Argos is very useful. I use it to mount/unmount external drives, display power consumption, control VPN, a simple application launcher. Argos claims compatibility with BitBar. Argos claims to support JavaScript Gnome Shell execution -- I have no reason to doubt this (as Argos itself is a JavaScript Gnome Extension). I highly recommend Argos for Gnome 3 users.

Thank you! You won't believe that I've been looking for just this tool for the last several months (I've been searching along the lines of "i3 status bar for gnome-shell" but was unsuccessful).

Using argos with zenity let you provide inputs from prompted dialog in gnome make it feels like professional taskbar item :) you may find it tricky to execute a function inside your argos script and i found a simple way to make it works is to call the script itself and provide arguments to it. I wrote it here in my blog if you want a quick example to get started .

http://blog.ebfe.pw/posts/argos.html