A mostly complete guide to React rendering behavior (2020)

My current ongoing Redux maintenance task is trying to revamp our "Redux Essentials" tutorial to be TS-first. Making slower progress on that than I'd wanted, but hopefully can get that wrapped up in the not _too_ distant future.

Beyond that, we've got a ton of open RTK Query feature requests that I'd like to address later on this year.

the moment you have to keep track of any type of state, managing dozens of UI elements quickly becomes extremely tedious.

This is exceedingly complex, error prone (because you might miss parts of the state that should change) and often slow (because you tend to overcorrect).

I think if more people would do this exercise they would find that they don't need it, or at least that they might need some form of state reconciliation, but not enough to really warrant all the complexity the tool introduces. Some will find that they don't need it but will still use it for other reasons, like familiarity or because that's what their team uses.

Sprinkle it a bit with some simple JavaScript/jQuery code for animations, forms checking etc, if you want. That's it. That's how it was supposed to work and that's how it works best. JavaScript was made to make the monkey dance. The end result, either made with overcomplicates frameworks like React/Angular or with simply generating the web page on the backend, is irrelevant to the user.

Imagine a world where you just had drawing and input handling primitives on the web. You wouldn't invent the DOM and then something like React to wrangle it that's for damn sure.

Like, they know how to do a simple HTTP query in C/go whatever, and then don’t understand why would you need the whole complexity of spring.

It just turns out that the real world is more complex than what they assume - and they are often more than aware of that in their specific subfield.

C++ always seems to me pretty absurd just because C++ people don't seem to know better ways, and seem to think to much about squeezing out the least little bit of performance instead of aiming for simple abstractions that are performant enough. Also, the last 40 years of programming language development seems to be unknown to them, or at least doesn't influence their decisions, or if they pick up a new idea, it's implemented in the most possible awkward way (because, again, performance).

Everything in that post should still be 100% accurate and relevant.

I specifically did _not_ try to go into further details on Suspense or some of the intricacies of Concurrent Rendering (beyond "React can cancel or reset those render passes"). My overall goal was to explain the core mental model of how React's basic rendering works on the client side.

As far as Suspense goes, that can be summarized as "throw a promise while rendering, `<Suspense>` acts like a `try/catch` at the component level, React will re-render this component when the promise resolves and from its perspective that function call _always_ returned the data synchronously".

Concurrent Rendering is really complicated internally, but loosely: React has an internal notion of priorities for queued renders. `startTransition`, `useDeferredValue`, and Suspense all mark renders as low priority, so those render passes can be "rebased", interrupted, or canceled as needed based on updates that come in later.

That said, React Compiler will _depend_ on React 19, because it needs a new memo/caching hook that will be included in 19.