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

1. Reproduce or describe the slowdown.
2. Identify what triggers re-renders (state updates, props churn, effects).
3. Isolate fast-changing state from heavy subtrees.
4. Stabilize props and handlers; memoize where it pays off.
5. Reduce expensive work (computation, DOM size, list length).
6. 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.