Use Luxon in a notebook

I’d like to use the Luxon library in my notebook. But when I add a require statement:

luxon = require('luxon');

I receive the error

luxon = RequireError: invalid module

This syntax works for me if I try to import the Moment.js library instead. Is there a restriction on which libraries can be imported to Observable? Or is it because perhaps Moment.js is packaged differently than Luxon?

Check out the Module Require Debugger: