This is the UZIP.js library provided as an ES module.

import UZIP from 'https://tomashubelbauer.github.io/esm-uzip-js/index.js';
// Usage as per https://github.com/photopea/UZIP.js#interface

This repository updates its UZIP.js submodule automatically every day and while doing that copies the UZIP.js file from it to index.js appending export default UZIP; to make it a valid ES module.

A GitHub Actions workflow is used to accomplish that: .github/worflows/update.yml

You can check it to see when it last run as well as click through the submodule to the UZIP repository to see that the submodule is up to date with that repo.

GitHub Pages are used to serve the contents of the repository, this is better than using the Raw option on GitHub, because the file also has a correct MIME type and thus can be used as an ESM module.

I've rethought adding them and they have polluted the history somewhat.