TinyMCE 5.9 has been released, and the headline Real-Time Collaboration feature was written in ReScript 
(with Haskell for the server)
(we’re still using ReasonML syntax - the project started in September 2019, long before ReScript existed - but we will probably convert the syntax the coming months)
It’s a pretty substantial codebase now:
github.com/AlDanial/cloc v 1.90 T=0.37 s (2847.5 files/s, 398065.4 lines/s)
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Language files blank comment code
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ReasonML 781 9307 950 85589
The bulk of the client-side code was written by two people. ReScript productivity gains are real, folks.