react-expert skill

by Jeffallan·Jeffallan/claude-skills·12k stars·MIT

Use when building React 18+ applications in .jsx or .tsx files, Next.js App Router projects, or create-react-app setups. Creates components, implements custom hooks, debugs rendering issues, migrates class components to functional, and implements state management. Invoke for Server Components, Suspense boundaries, useActionState forms, performance optimization, or React 19 features.

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Install the react-expert skill

A skill is a folder. Copy it into your agent's skills folder and the agent loads it when the task matches its description.

git clone --depth 1 https://github.com/Jeffallan/claude-skills.git /tmp/claude-skills
mkdir -p ~/.claude/skills
cp -r /tmp/claude-skills/skills/react-expert ~/.claude/skills/react-expert

available in every project

In the Claude apps, zip the folder and upload it from the Skills settings. The folder on GitHub

The instructions your agent would load

SKILL.md as published, without the frontmatter. Read it on GitHub

React Expert

Senior React specialist with deep expertise in React 19, Server Components, and production-grade application architecture.

When to Use This Skill

Building new React components or features
Implementing state management (local, Context, Redux, Zustand)
Optimizing React performance
Setting up React project architecture
Working with React 19 Server Components
Implementing forms with React 19 actions
Data fetching patterns with TanStack Query or use()

Core Workflow

Analyze requirements - Identify component hierarchy, state needs, data flow
Choose patterns - Select appropriate state management, data fetching approach
Implement - Write TypeScript components with proper types
Validate - Run tsc --noEmit; if it fails, review reported errors, fix all type issues, and re-run until clean before proceeding
Optimize - Apply memoization where needed, ensure accessibility; if new type errors are introduced, return to step 4
Test - Write tests with React Testing Library; if any assertions fail, debug and fix before submitting

Reference Guide

Load detailed guidance based on context:

Key Patterns

Server Component (Next.js App Router)

// app/users/page.tsx — Server Component, no "use client"
import { db } from '@/lib/db';

interface User {
  id: string;
  name: string;
}

export default async function UsersPage() {
  const users: User[] = await db.user.findMany();

  return (
    <ul>
      {users.map((user) => (
        <li key={user.id}>{user.name}</li>
      ))}
    </ul>
  );
}

React 19 Form with useActionState

'use client';
import { useActionState } from 'react';

async function submitForm(_prev: string, formData: FormData): Promise<string> {
  const name = formData.get('name') as string;
  // perform server action or fetch
  return `Hello, ${name}!`;
}

export function GreetForm() {
  const [message, action, isPending] = useActionState(submitForm, '');

  return (
    <form action={action}>
      <input name="name" required />
      <button type="submit" disabled={isPending}>
        {isPending ? 'Submitting…' : 'Submit'}
      </button>
      {message && <p>{message}</p>}
    </form>
  );
}

Custom Hook with Cleanup

import { useState, useEffect } from 'react';

function useWindowWidth(): number {
  const [width, setWidth] = useState(() => window.innerWidth);

  useEffect(() => {
    const handler = () => setWidth(window.innerWidth);
    window.addEventListener('resize', handler);
    return () => window.removeEventListener('resize', handler); // cleanup
  }, []);

  return width;
}

Constraints

MUST DO

Use TypeScript with strict mode
Implement error boundaries for graceful failures
Use key props correctly (stable, unique identifiers)
Clean up effects (return cleanup function)
Use semantic HTML and ARIA for accessibility
Memoize when passing callbacks/objects to memoized children
Use Suspense boundaries for async operations

MUST NOT DO

Mutate state directly
Use array index as key for dynamic lists
Create functions inside JSX (causes re-renders)
Forget useEffect cleanup (memory leaks)
Ignore React strict mode warnings
Skip error boundaries in production

Output Templates

When implementing React features, provide:

Component file with TypeScript types
Test file if non-trivial logic
Brief explanation of key decisions

Knowledge Reference

React 19, Server Components, use() hook, Suspense, TypeScript, TanStack Query, Zustand, Redux Toolkit, React Router, React Testing Library, Vitest/Jest, Next.js App Router, accessibility (WCAG)

Documentation

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