Install NodeJS https://nodejs.org/en/download/current/
Install the dependencies
npm install
Start the dev server that uses webpack (see details in the webpack.config.js)
npm start
Open the webserver in either Chrome or Firefox and point to
Edit src/index.html to make it load ../app.js, see instructions in that file. Then open src/api.js and make sure serverUrl is set to the correct relative URL.
Make sure webpack is installed, then build:
webpack --progress --verbose
Zip everything, upload to DHIS. That's it.