Be sure that Python 3 is installed (for building the 3rd party library) and that you have installed Rollupjs globally `npm i rollup -g`.
To build the two iwmlib files type `npm run build`. The files will be generated in the dist folder (iwmlib.js and iwmlib.pixi.js). If you want to watch the files for a continuously build type `npm run watch`.
To build the 3rd party library type `npm run 3rdparty`. The file will be generated in the dist folder (iwmlib.3rdparty.js).