We constantly hit snags that could have been caught by a proper type system, but TS just was not there in 2017. In late 2019 it finally had good support for functional programming constructs, such as those needed to describe HOC in React. Elm is great and probably a better choice when starting a fresh project than megaslow TypeScript, but when you already have 50 KLOC of source code written in JavaScript, using libraries such as Redux and React, you do not have that luxury.