Hi,
I'm a web developer since 15 years , interested in all GIS tools and in particular on ESRI solutions.
I would like to improve my skill on this solutions.
Welcome to the community!
Here are a few great places to check out for web development:
ArcGIS Web AppBuilder
Web AppBuilder custom widgets
https://community.esri.com/t5/web-appbuilder-custom-widgets/gh-p/web-appbuilder-custom-widgets