The readme tells you everything you need to know. In fact it clearly says that it runs BOTH a server (index.js) and a client (index.html). The server servers up the web page but otherwise doesn't seem to interact. The server also provides MQTT integration.
So the easiest thing to do would be to run it according to the instructions - separate to Node-RED. Then use it to do a few things and monitor your MQTT Broker to see what message topics it is using. Then you can send those topics from Node-RED.
After that, pull apart the code and translate it to Node-RED. It isn't doing anything that you couldn't easily do in Node-RED.