I like F# and believe the author has done an amazing job evolving a functional language on the dot net platform but there are simply too many design choices in F# geared around C# compatibility and limitations of CLR being an object oriented language that when you switch to a different compilation target, these language aspects begin to look like bizarre warts.
Things like limitations on statically resolved type parameters being supported only for inline functions, etc. don't make sense for a language targeting javascript.
It is interesting to note that F# took a lot of concepts from OCaml but stripped out functors, structural typing support etc. to adapt to dotnet. These adaptations are largely required because Microsoft does not treat F# as a first class citizen (at the same level as C#) and CLR is very explicitly geared towards object oriented languages. An occasional endorsement from Microsoft does not magically obliviate these deeply ingrained design decisions in F#.
When targeting javascript these adaptions become really pointless. As demonstrated by Microsoft's own TypeScript language, Structural typing can be quite useful for interop.
It would be really nice if F# was a first class citizen in dotnet world and javascript was a first class compilation target maintained by the F# core team adapting the language to javascript target in the same way it currently adapts to dotnet. However that is not the present day reality. However typescript, despite being a javascript superset (and inheriting all its warts) has a really flexible type system and lends itself well to functional programming (as demonstrated by Giulio Canti's fp-ts [1] project).
Unlike ReasonML, however, typescript's type system is not sound. I have written a more detailed comparision [2] of TS and ReasonML. I do actively use TypeScript for my day job and mostly love it, but I am much more optimistic about ReasonML once the ecosystem matures.
tl;dr: The 80% best practices parity between ReasonML and modern functional javascript which the "What & Why" page of official documentation [3] talks about, does not exactly hold true for F#. So, while it is not that F# is not a great language, or that you can't build great apps with F#, however, as it currently stands, I don't see any compelling advantages of preferring F# over ReasonML, unless your backend is also F# and you want to (and can) share code between frontend and backend.
My familiarity with both F# and ReasonML is quite early stage (a few weeks each) and so would welcome any corrections.
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[1] https://github.com/gcanti/fp-ts
[2] https://lorefnon.tech/2018/05/13/reasonml-vs-typescript-firs...
[3] https://reasonml.github.io/docs/en/what-and-why.html