It looks like xml2js is only published in CommonJS intended for Node, so you’ll need something like bundle.run or wzrd.in to convert it into a browser-friendly format. We normally recommend bundle.run, but it currently appears to be down and serving 503 errors. Fortunately, wzrd.in does currently appear to be working:
If you want your notebook to work even if bundle.run or wzrd.in is down (as these services are generally much less reliable than our normal npm-backed CDN of choice, jsDelivr), you can attach the bundled library as a file to your notebook and load it that way. For example: