React Component Performance

Overview

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

references/examples.md