How can I use the function utf8tob64u in pmlib.rs.KJUR in my Postman scripts?

How can I use the function utf8tob64u in pmlib.rs.KJUR in my Postman scripts?

Details (like screenshots):

I would like to use the following function in my script: jsrsasign JavaScript API Reference - global__ (kjur.github.io)

I can successfully call pmlib.rs.KJUR.jws.JWS.sign(null, header, payload, key) for example, but I would like to use some functions from the globals__

This is described on the libraries homepage postman-util-lib | 🚀 A crypto utility library to be used from Postman Pre-request and Tests script tabs.

const result = pmlib.rs.utf8tob64u('My amazing string')