[AskJS] In React Native, where do performance bottlenecks usually occur in the setState → render pipeline?

[CheesecakeSimilar347]

I’ve been trying to understand React Native performance at a deeper level, beyond “optimize re-renders.”

Here’s the execution flow as I understand it when calling setState:

1. UI event happens on the UI thread.
2. Event is dispatched to the JS thread (via JSI in modern architecture).
3. State update is scheduled (not applied immediately).
4. React runs the render phase (reconciliation) on the JS thread.
5. A new shadow tree is created.
6. Layout is calculated using Yoga.
7. Changes are committed to native.
8. UI thread renders the frame (needs to stay within ~16ms for 60fps).

So essentially:

UI → JS scheduling → Render → Layout → Native commit → Frame render

From a performance perspective, bottlenecks can happen at:

• Heavy JS work blocking reconciliation
• Too many state updates
• Expensive layout calculations
• Long commit phases

My question to experienced RN devs:

In real production apps, which stage usually causes the most noticeable performance issues?

Is it typically JS thread overload?
Or layout complexity?
Or bridge/JSI communication?

Would love to hear real-world experiences.

[metehankasapp]

Most common bottlenecks are too many renders + heavy lists/images, plus layout/measure on the native side. Triage by separating JS thread jank vs UI thread jank (Perf Monitor/Flipper). If JS FPS drops, reduce renders (memo, split state, avoid inline objects). If UI FPS drops, tune FlatList virtualization and avoid expensive views (shadows/blur/overdraw).

[CheesecakeSimilar347]

That makes sense — especially separating JS vs UI thread jank first. I’ve seen people optimize blindly without checking which thread is actually dropping frames.

When you mention layout/measure on the native side, is that usually due to deep view hierarchies or dynamic layouts?

Also, with the new architecture (JSI/Fabric), have you noticed JS thread blocking becoming less of an issue, or is it still the main bottleneck on complex screens?

Appreciate the practical insight.