TypeScript 4 released recently and the most interesting new feature is variadic tuple types. They have a lot of promise for functional programming in TypeScript, as they enable really sophisticated typing of the arguments of higher-order functions.
I recently refactored a personal project of mine written using React & Redux. I've been thinking a lot recently about how to organize reducers. Previously I utilized the reduce-reducers library, and organized my reducers both temporally and structurally. That proved untenable in the long run.