Kitty,
There is a migration page that I suspect will become substantially larger as time goes on - Migrating from 3.x to 4.0 | ArcGIS API for JavaScript 4.0
I will be honest, this is a little scary:
Consider rewriting applications instead of simply trying to update them. |
For those of us that have spent several years developing and enhancing a mapping application, using many custom modules and classes, this sure sounds painful!
And, with the functionality of 3.x not yet ported over, it may be difficult to start that process now. I understand why this must occur, I just hope that 3.x will receive bug fixes and be supported well into the future while we make the transition. I suppose the silver lining is job security!