@davout_uk I am afraid you won’t be able to do that.
You can give this a read: https://learning.getpostman.com/docs/postman/scripts/postman_sandbox/
There are a few popular inbuilt libraries that you can use which are documented in the above mentioned link.
One way I have seen as a workaround is that you hit the CDN / url of the library using Postman and then you can use
JSON.stringify and store the JS library code in an environment variable.
Then you can just do a
eval on the environment variable in any request and use all the functions of the library.
This is just a workaround.