My app always requires a sub command, e.g.

node main.js sub1
or
node main.js -x sub1

It's not valid to do

node main.js
or
node main.js -x

How can I catch this scenario? Is there a way to introspect the program object to tell if a sub command was used?

I was going to use process.argv.length but that doesn't really work because a user could still pass in options without a sub-command (node main.js -x -y -z). I can get around that by parsing porcess.argv more carefully but I was hoping there was a more supported way.