First, make sure you have the current version of nodejs.
Download the levels:
wget -P levels http://gtamp.com/mapscript/_singleplayer/04_gta2files/extras/singleplayer/data/{wil,bil,ste}.{sty,gmp}
To install dependencies:
npm install
For development:
npm run watch
# Open another shell and run:
node server.js
For production:
NODE_ENV=production npm run build
node server.js