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mike douges
@douges.dev

This behavior made me think there was a perf regression when upgrading to React 19: github.com/facebook/rea.... Turns out it was because transitions weren't firing anymore (behavior change?) and then the 300ms fallback being shown made it look slow.

github.com[React 19] Suspense throttling behavior (`FALLBACK_THROTTLE_MS`) kicks in too often · Issue #31819 · facebook/reactReact version: 19.0.0 Related Issues: #30408, #31697 This may be the intended behavior, but I'm opening this issue anyway because enough discussion hasn't been done in the related issues IMO and th...

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mike douges
@douges.dev

The transitions not firing was interesting. In React 18 I had a transition start that was technically async (start transition -> iframe message -> get message back -> set state to trigger suspense). In React 19 that doesn't work anymore.

Ricky
@ricky.fm

Yeah, this is a controversial one but I think the tradeoff off makes sense if you consider the UX without it.

Ricky
@ricky.fm

The principle is that if you paint a loading state to the user, you should show it for a small amount of time so the user can at least see the fallback instead of seeing flickers in the UI.

Ricky
@ricky.fm

As devs we care a lot about raw perf, but UX research shows that flickering is perceived as slower than showing a loading state (to a point). Slower is sometimes better. So yes the throttling is a perf tax, but it’s a UX gain.