We tried ReScript 2 years ago at work when it was still in its infancy, and still named ReasonML. Besides many other gripes at the time, one of the biggest pain points was the lack of any async/await support, and a very cumbersome Promise wrapper.
Unfortunately, it looks like not much has changed[0], and you’re still forced into writing the equivalent of unwieldy Promise chains.
I ended up migrating us onto Typescript, which was a great move for us. The seamless interop with JavaScript combined with the massively active community makes it a no-brainer over other attempts at strongly-typed JS, IMO.