That's really not how you'd write a large idiomatic React application.

That's a bit No True Scotsman for me. Just in the replies to my previous comment, there are several quite clear yet apparently contradictory views expressed about how these things are supposed to work. I doubt that anyone, probably including the React developers themselves, yet has enough experience to sensibly determine what is and isn't idiomatic or best practice here. In any case, I'm far more interested in effective results than dogma, which is why we've been doing practical investigations into what really happens when the tools are used in different ways.

Conceptually, you should be running render() methods on the actual items which have changed, and a very small number of parent components with little-to-no DOM elements. You should also be executing a relatively small number of shouldComponentUpdate() methods which should be extremely fast to execute.

And this is where the assumptions started breaking down in our experiment.

For one thing, we have a somewhat complicated data model and a somewhat complicated UI to present it. Managing the relevant shouldComponentUpdate mechanisms was getting tedious even in our short term experiment. If you're rerendering top-down in a heavily nested UI then it seems you need to provide shouldComponentUpdate in quite a lot of places just to deal with the parent-child relationships with acceptable efficiency, and each of those implementations is a potential source of errors because now you have multiple sources of truth.

Also, for things that aren't extremely fast to execute because they rely on derived data, you wind up with questions of what intermediate results to cache and where. Caching intermediate results goes against the kind of approach much of the React community seems to advocate, hence props in getInitialState being an antipattern and all that.

Time will tell, but once the abstraction started leaking in these kinds of ways, it wasn't clear to us that trying to follow the pure, declarative approach that a lot of React advocacy promotes was really better than other strategies.

If you are doing that, then where exactly was the performance bottleneck, and how was your alternative approach avoiding it?

Bottlenecks were as above, among others.

Avoiding them comes down to the simple principle that if each component attaches to listen to events in a modular way and sets its own state accordingly, then the default is essentially not to rerender anything and has zero overhead. As soon as you start making active decisions about what to rerender, you immediately have the overhead of those decisions to worry about, and sometimes that overhead is significant if you're, say, responding to every character typed in a text box.

If you respond at a more local level, you can choose the granularity of responses to keep the overheads more controlled, which it seems so far is effectively getting the best of both worlds.

In fact, it sounds like your second approach might be closer to a normal idiomatic React app than your first implementation. Incidentally, are you using some sort of flux architecture?

In the sense that user interactions send meaningful messages to an internal component, that component is responsible for updating some stored data accordingly, and the internal component then signals changes that other parts of the UI can respond to, yes, it's somewhat like Flux in overall architecture.