This series of videos presented by GISman Lee will show how to develop a customised hierarchy-layer widgets in new ArcGIS Experience Builder with React.js, ArcGIS Javascript API & Reactstrap, as well as how to deploy Customised ArcGIS Experience Builder App on ArcGIS Enterprise.
Let's start moving from the old ArcGIS Webapp Builder to the new esri product. Initially 3 parts in total, maybe more in future.
https://www.youtube.com/watch?v=A-D0wAD1jUA