[gherkinnn]

fp-ts [0] and the accompanying io-ts [1] are very well designed and neatly implemented. I'd consider them the reference for all things FP in Typescript.

In practice though I find that they don't mesh well with the language and ecosystem at large. Using them in a React/Vue/Whatever app will catch you at every step, as neither the language nor the frameworks have these principles at their core. It takes a lot of effort to escape from their gravitational pull. Using Zod [2] for your parsing needs and strict TS settings for the rest feel more natural.

It could work in a framework-agnostic backend or logic-heavy codebase where the majority of the devs are in to FP and really want / have to use Typescript.

0 - https://gcanti.github.io/fp-ts/

1 - https://gcanti.github.io/io-ts/

2 - https://zod.dev