Modularize JS code

[mvahowe]

I took the ChatGPT JS and

• changed variable names to camelCase
• changed to fs-extra and added path modules in an opinionated way
• moved the algorithm to a file separate from the script
• reorganised the repo hierarchy so that the js code could use a single package.json file
• made DOM and string XML variants as the previous name didn't accurately describe the input values
• remove the try in the script so that the error message was useful