I know that Facebook's Typescript competitor, Flow, was both written in OCaml and tried to introduce the HM type system into the JS world. It was quite popular

I know that Facebook's Typescript competitor, Flow, was both written in OCaml and tried to introduce the HM type system into the JS world. It was quite popular back in the day, but eventually lost the war to TS. Perhaps more notably, they are still actively working on Rescript (formerly ReasonML), which is an Ocaml dialect with JS as the primary compilation target (think Clojurescript but Ocaml). They also maintain a flavor of React specific for Rescript. I don't know how much they dogfood it, but it seems like they're at least somewhat betting on an ML future. Disclaimer: Not a FB/Meta employee