[jey]

I'm diving into Reason now and it seems great. It seems like "Flow done right" -- about a year ago, I did a study of both Flow and TypeScript, then picked Flow because it seemed more principled and expressive. But it turned out that bolting Flow onto Javascript left it with a lot of edge cases and some oddities, but Reason instead avoids that by compiling to javascript instead of being bolted atop Javascript.

tldr: Reason is better than both TypeScript and Flow and has equally good interop with native untyped Javascript code.