What scenario can you think of where you have state updates while the user is scrolling?
1) We had a querying interface that would allow the user to construct a query and then it would return potentially thousands of results, asynchronously, over a websocket. We only displayed the first 300 on screen at a time, but sometimes the updates would come in so rapidly during that first 300 that one render wouldn't be finished before more results were available and the next render triggered. Things would get really backed-up and the UI would hang for multiple seconds at a time. So we decided to throttle the rendering - get the results as fast as possible, but only render once every 500ms or something. But during this time the user still might want to scroll around and look at other parts of the page, so we didn't want it to pause for 100ms every 500ms. It was a constant battle to keep things responsive while all this was going on.
2) We had another screen that would load another massive list (thousands and thousands) of entities as soon as you visited. These also came in gradually over time to spare the user from waiting for the last result before they could see the first. Similar deal: we throttled, but we needed to keep things responsive even during that throttling because the user would be scrolling up and down the results as they were coming in.
I never claimed that switching languages would have magically solved all our problems, but in our case it could've been a significant boon to performance which could've been one factor of many that contributed to a solution, and I just can't figure out why you have such a problem with that idea.
I am a data engineer now and sometimes have to build web interfaces for scrolling large data tables. Just like in the 3d graphics world, the trick to responsiveness is culling. Only download and display the amount of data that the user will see at a given time, plus some overhead so the user never sees gaps when scrolling.
While Rust may have solved the problem in #1, it is unlikely to solve the problem in #2 because you are also fighting the network where Rust is useless. Need culling.
There are some edge cases where these techniques can work - like if you have a really simple layout, and you can give a fixed-height to every item (table row or otherwise), and you assume the user is never going to resize their browser window - but it isn't nearly as obvious of a win as it is for 3D rendering and we just never decided it was worthwhile to try going down that rabbit-hole.
Exactly the same for 3d graphics. The auto-positioning is different but conceptual similar.
Yes B is my recommended approach. Since we are talking about performance, we should really be putting limits on what fast and slow mean. That is because it doesn't really matter if something is fast or slow, what matters is the performance difference between different approaches.
For B on average, performance will in the microsecond range, DOM rendering will be in the millisecond range, and the network is >100ms to seconds range. It is unlikely that B will be equal or slower to brute force rendering everything. Those X microseconds spent figuring out the culling window saves Y milliseconds rendering and saves Z milliseconds to seconds querying the network.
Most "performance" problems on the web are solved by simple techniques like virtualization, pagination, pushing expensive calculations to the server, avoiding round-trip requests, or basic UI/UX improvements. The only time I would care about JavaScript's actual runtime performance if I were doing something crazy like 3d rendering in the browser and that's a completely different set of problems than React or Yew are set up to handle.