I'm using Slate window manager and I wanted a way to create a new space on El Capitan using script. I have found other solutions like the following, but it doesn't work on El Capitan.
list 1 would contain all the spaces, but
add new desktop
and I didn't find any
list 2 which would contain
add new desktop.
do shell script "open -a 'Mission Control'" tell application "System Events" of list 1 of group 2 of group 1 of group 1 of process "Dock" end tell tell application "System Events" to key code 53