| name | react-component-performance |
| description | Analyze and optimize React component performance issues (slow renders, re-render thrash, laggy lists, expensive computations). Use when asked to profile or improve a React component, reduce re-renders, or speed up UI updates in React apps. |
React Component Performance
Overview
Identify render hotspots, isolate expensive updates, and apply targeted optimizations without changing UI behavior.
Workflow
- Reproduce or describe the slowdown.
- Identify what triggers re-renders (state updates, props churn, effects).
- Isolate fast-changing state from heavy subtrees.
- Stabilize props and handlers; memoize where it pays off.
- Reduce expensive work (computation, DOM size, list length).
- Validate with profiling; avoid speculative changes.
Checklist
- Measure: use React DevTools Profiler or log renders; capture baseline.
- Find churn: identify state updated on a timer, scroll, input, or animation.
- Split: move ticking state into a child; keep heavy lists static.
- Memoize: wrap leaf rows with
memo only when props are stable.
- Stabilize props: use
useCallback/useMemo for handlers and derived values.
- Avoid derived work in render: precompute, or compute inside memoized helpers.
- Control list size: window/virtualize long lists; avoid rendering hidden items.
- Keys: ensure stable keys; avoid index when order can change.
- Effects: verify dependency arrays; avoid effects that re-run on every render.
- Style/layout: watch for expensive layout thrash or large Markdown/diff renders.
Optimization Patterns
- Isolate ticking state: move a timer/animation into a child component so the parent list does not re-render every tick.
- Stabilize callbacks: prefer
useCallback for handlers passed to memoized rows.
- Split rows: extract list rows into memoized components with narrow props.
- Defer heavy rendering: lazy-render or collapse expensive content until expanded.
- Prefer derived data outside render: compute summaries with
useMemo or helper functions when inputs are stable.
Example Reference
Load references/examples.md when the user wants a concrete refactor example.
