Esri recently released version 4 of the ArcGIS Server JavaScript API - see https://developers.arcgis.com/javascript/ and https://developers.arcgis.com/javascript/latest/guide/choose-version/index.html
This is a substantial re-write compared to version 3.x with seemingly every class, method and event receiving an update. There are also new functions relating to 3D web maps.
Errors, questions and problems for this version are likely to be different compared to version 3.x. Do we need a new GIS-SE tag to handle this?