Pretty sweet if I understand that this is a front-end for the OCaml compiler! This means you could run your typed JS on OCaml's runtime instead of Node.js. Granted, the availability of npm packages will be small since most of them aren't typed by Flow but in theory you could use OCaml libraries?

Or you could just write Reason I suppose. :) There's a crazy permutation of ways to write code that can run in a browser or server run time these days!