There are a lot of useful samples for the ArcGIS API for JavaScript.
https://developers.arcgis.com/javascript/jssamples/Unfortunately, once a widget is customized for the Web AppBuilder, it cannot be uploaded back to my
hosted AGOL site; it can only be deployed on my own server, which somewhat defeats the purpose.
If all JS samples were available as widgets directly out of the Web AppBuilder, it would make it 100x more useful.