A modern programming language that makes developers happier.

kotlinlang

Possibly... At this stage I was just hoping for a sandbox where I could edit/run/debug my webapp quickly within IDEA without extra dependencies/build config. <https://kotlinlang.org/docs/tutorials/javascript/getting-started-idea/getting-started-with-intellij-idea.html> shows how to do that, but the index.html example ends up with URLs like src="out/production/sampleapp/sampleapp.js", which isn't much use for eventual production code.