Check out https://reasonml.org - created by Jordan Walke, the creator of React. Reason offers the best of both worlds - type safety without getting in the way and faster JS than what you'd write by hand.
As much as I would shill reasonml. Think before you adopt - it still requires more upfront work than typescript (you will have to write bindings for most things even popular stuff. You might end up fighting it too.) but as parent said, you get more expressiveness (algebraic types, powerful pattern matching, immutability, partial application etc) and sound type system with a speedup on both transpile times and actual run time.
You can leverage ocaml/ml as well as js ecosystem. Mix different files and syntax.
To add to this, there are at least 3-4 pain points which... are just a pain with ReasonML, that can kinda counteract its type system.
- non-standard ordering of arguments between belt/standard library
- Ocaml's standard library actually generally avoiding the Option/Result type, in preference of exceptions, which is unexpected and a pain since it's an ML.
- package management involves manually adding things to the bsconfig (has this changed?)
- things randomly break between relatively minor Bucklescript versions, they broke something pretty important in like a .x release when I was messing around with it
- server side isn't good. It technically works but all the bindings are old or terribly documented, and you never really know if it's not going to blow up at some point.
Otherwise, I actually quite like it! None of those are actual core language complaints.
Slightly off topic but has anyone tried Hegel? https://github.com/JSMonk/hegel, looks like a nice mix of reason,ts and flow. It's just Js with types + type inference.
You can leverage ocaml/ml as well as js ecosystem. Mix different files and syntax.
Bsb is also faster than tsc.