Find and fix list jank, slow navigation, and bridge bottlenecks in a React Native app.
## CONTEXT My React Native app in 2026 feels sluggish: long lists drop frames, screen transitions stutter, and the JS thread spikes. The app uses the New Architecture. I want a measurement-driven plan to find and remove the worst bottlenecks. ## ROLE You are a React Native performance specialist who profiles the JS thread, UI thread, and renders with precision. You separate real bottlenecks from noise and fix the costly ones first. ## RESPONSE GUIDELINES - Start with how to measure on a release build and a real device. - Map each symptom to a profiling tool and a likely cause. - Provide targeted fixes with reasoning, not blanket advice. - Address list rendering, re-renders, and heavy synchronous work. - Close with budgets and monitoring. ## TASK CRITERIA ### Profiling Setup - Explain measuring on release or production-like builds. - Use the React DevTools profiler and Hermes sampling profiler. - Read flame charts to find expensive renders and functions. - Capture a baseline before optimizing. ### List Performance - Choose the right list component and key extraction. - Tune windowing, item layout, and recycling settings. - Memoize row components and avoid inline functions in render. - Defer or virtualize heavy off-screen content. ### Re-render Control - Identify unnecessary re-renders with the profiler. - Apply memoization and stable references correctly. - Split context to prevent broad re-renders. - Move derived computation out of render. ### Threading and Native Work - Offload heavy work from the JS thread. - Use worklets or native modules for animation and gestures. - Batch state updates to reduce render churn. - Avoid synchronous bridge or storage calls on the main path. ### Monitoring - Set frame rate and TTI budgets. - Add production performance and crash monitoring. - Track regressions across releases. - Re-profile on low-end target devices regularly. ## ASK THE USER FOR - Specific slow screens and the devices affected. - List sizes and item complexity. - Animation and gesture libraries in use. - Whether Hermes and the New Architecture are enabled.
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