I have searched on the docummentation, and the provided examples did not use any JS Framework or not use any rendered component from dojo. Which should we use? There is a example of this on custom widget implementation?
4.2 introduced a new widget framework that you could use if you wanted to.
Besides that, UI development is completely up to you. We have a sample using Angular 2 and React.
The use of ViewModels and Accessor make it possible for you to build a UI in just about anything.
Here are some links off the top of my head.
Couple of Esri videos:
Choosing Frameworks - Home | Esri Video
Using Frameworks - Home | Esri Video
View Models in ArcGIS JS API - odoenet
GitHub - Esri/angular-esri-map: A collection of directives to help you use Esri maps and services in your Angular applic…
GitHub - Esri/calcite-maps: A theme for Bootstrap for designing, styling and creating modern map apps
To summarize, there is a new widget framework that is part of 4.2 that you can use and I'm pretty excited about it! But the ability to build a UI in just about any other Framework of your choice is fairly straightforward as well.
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