I was not aware of ReScript so I looked it up only to discover it’s part of the React tool chain. I am really of the opinion that React is the new jQuery.

The definition of mission critical is also misplaced. When I think of mission critical I think of Ada and Rust for something like running a nuclear power plant or dashboard of a fighter aircraft. In those cases failure is expensive and deadly, so code that works is an insufficient quality. The definition here though is shipping code that must work. Why would anybody ship code that doesn’t work?