Really understanding those properly and deeply can take a lot of time, though. I've been using it professionally for almost two years at this point and some of those hooks I'm still a bit shaky on (although we don't use them that often, and probably less often than we should). And I just learned a couple more new things in the 'You might not need an effect' article that was posted here the other day (I already do most of those, but not all of them).

And I manage several junior developers and I've seen them struggle to understand all of these, even over many months including pair programming and code review feedback.

That being said, I was able to jump into an existing codebase and be useful in about a week with very little prior knowledge of React (just some dabbling in React Native pre-hooks), so I don't think it's hard to learn enough to start doing useful things with it, especially if you already know Javascript/Typescript.

And I would agree that I've struggled much more with other React libraries than core React itself. It's been a long time since I've had to look anything up for core React hooks, I can write lots of React code (in Typescript) and be relatively confident it will work as intended, barring some dumb mistake I made or a misunderstanding of how the data flows in the existing codebase, as long as it compiles.

Agreed, it employs a lot of good functional concepts and shifts you into another kind of "reactive" thinking, where the render function is a pure representation of its state. This actually allows you to "declare" your state and its mutations in a way that perfectly executes your business logic and presents it in a single pure function, but generally, it's hard to think with pure functions for some reason, and side effects are imminent, as well as some asynchronous black-boxed action takes place. Actually – for many, side-effect becomes a patch for conceptual blanks in knowledge about functional data flow in its pure form, and you can tell who really understands it just by looking at his side-effect usage. In the end, what makes the library so appealing is that you need just 6 basic hook functions aligned together in a proper way to describe any kind of state and functionality user interface needs, and it actually performs top-notch and takes little space.