DISCLAIMER: Please note that this is a prototype from 2017 that is not actively maintained anymore. If you are looking for the repository of the more recent Simple Query Builder, you can find it here.
You can find a demo version on https://tools.wmflabs.org/wd-query-builder/.
# install dependencies
npm install
# serve with hot reload at localhost:8080
npm run dev
# build for production with minification
npm run build