Hi Michael,
We need to update our parser for this to work. And we need remove Rhino also as it will not understand it.
Rhino is almost completely removed so that is not that much work left but the parser will be more work. A good thing is that we can add feature by feature. For example add "const" and "let" first and continue with the rest later.
I think you can import a modern javascript file into a Cappuccino app with @import "MyFavoriteJavaScript.js". This file should just be executed when the app is loaded. I have not tested this for a long time so I'm nor sure if it still works.
- Martin