• 1.15 doesn't work. 1.12.2 does. Didn't test other versions.
• Starting this project requires running both a server and a client. Use npm start in tab 1, and npm run build && npm run client in a second tab.
• The readme shows you need to put the map data in map. It needs to be in map/Qazzian1 (EG minecraft-mapper-js/map/Qazzian1/level.dat)
• In public/js/mapInterfaces/QazzianMapServer.js:5, change the io URL to the url of the socket.io server. (see below)
• This list is wrong, incomplete or incorrect. It did work for me this way. Maybe it's useful to you.

// public/js/mapInterfaces/QazzianMapServer.js:5
let socket = this.socket = ioInterface("http://localhost:4001");

For the curious, after loading for like 10 seconds, you get this:

This is a great proof of concept! Well done.