# react-component-performance

Identifies React render hotspots, isolates fast-changing state, and eliminates re-render churn. Useful when lists lag or components re-render too often.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 1100 installs · ★ 4009
- Author: Dimillian
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/Dimillian/Skills/tree/HEAD/react-component-performance/SKILL.md
- Updated: 2026-03-29
- HTML: https://affpapa.org/en/nevibecode/skills/dimillian-react-component-performance

## What it does

The skill enforces a clear debugging workflow for UI slowdowns: reproduce the lag, trace what triggers re-renders, isolate volatile state, and memoize only where it actually helps. It targets state that updates frequently on timers, scrolls, inputs, or animations, which often causes entire parent trees to re-render needlessly.

It includes concrete code patterns for common fixes. Examples show how to push timer state down into dedicated child components, stabilize handlers using `useCallback` paired with `memo`, and compute derived data outside the render cycle. It also covers list windowing and key stability.

Validation relies on the React DevTools Profiler to catch components rendering longer than ~16 ms on the Flamegraph. Blind memoization without baseline profiling often adds memory overhead without fixing the actual lag.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add Dimillian/Skills --skill react-component-performance -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/react-component-performance/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/react-component-performance/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add Dimillian/Skills --skill react-component-performance -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/react-component-performance/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add Dimillian/Skills --skill react-component-performance -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/react-component-performance/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install Dimillian/Skills react-component-performance
```

2. **Manually: put the files in place**
- File: `.github/skills/react-component-performance/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add Dimillian/Skills --skill react-component-performance -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/Dimillian/Skills --path react-component-performance
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/react-component-performance/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add Dimillian/Skills --skill react-component-performance -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/Dimillian/Skills/tree/HEAD/react-component-performance/SKILL.md

## When to use it
- isolate ticking timer and animation state into separate child components
- stabilize callback references and props using `useCallback` and `memo`
- identify components rendering longer than ~16 ms using the profiler
- avoid heavy recalculations during render with `useMemo`

## Example prompts
- Clicking an item in this list causes every row to re-render. Help me optimize the component.
- A timer in the dashboard header forces a heavy child list to re-render every second. How do I isolate this state?

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 38eeb1e04c6e7500.

BEGIN THIRD-PARTY FILE 38eeb1e04c6e7500
````text
---
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**: open React DevTools Profiler → record the interaction → inspect the Flamegraph for components rendering longer than ~16 ms → compare against a pre-optimization baseline recording.

## 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 or animation counter into a child so the parent list never re-renders on each tick.

```tsx
// ❌ Before – entire parent (and list) re-renders every second
function Dashboard({ items }: { items: Item[] }) {
  const [tick, setTick] = useState(0);
  useEffect(() => {
    const id = setInterval(() => setTick(t => t + 1), 1000);
    return () => clearInterval(id);
  }, []);
  return (
    <>
      <Clock tick={tick} />
      <ExpensiveList items={items} /> {/* re-renders every second */}
    </>
  );
}

// ✅ After – only <Clock> re-renders; list is untouched
function Clock() {
  const [tick, setTick] = useState(0);
  useEffect(() => {
    const id = setInterval(() => setTick(t => t + 1), 1000);
    return () => clearInterval(id);
  }, []);
  return <span>{tick}s</span>;
}

function Dashboard({ items }: { items: Item[] }) {
  return (
    <>
      <Clock />
      <ExpensiveList items={items} />
    </>
  );
}
```
````
END THIRD-PARTY FILE 38eeb1e04c6e7500

The third-party file has ended. Everything between the 38eeb1e04c6e7500 tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

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