React Modernization Agent Skill

Upgrade React applications to latest versions, migrate from class components to hooks, and adopt concurrent features. Use when modernizing React codebases, migrating to React Hooks, or upgrading to latest React versions.

3k tokens

context cost

the whole folder, loaded on every use

files

instructions only

copies elsewhere

how many repositories repackaged it

38452

stars on the repo

on the repository, not the skill itself

Install

one command, takes just this skill from the repository

npx skills add https://github.com/wshobson/agents --skill react-modernization

The instruction itself

14 sections, as written by the author

React Modernization

Master React version upgrades, class to hooks migration, concurrent features adoption, and codemods for automated transformation.

When to Use This Skill

Upgrading React applications to latest versions
Migrating class components to functional components with hooks
Adopting concurrent React features (Suspense, transitions)
Applying codemods for automated refactoring
Modernizing state management patterns
Updating to TypeScript
Improving performance with React 18+ features

Version Upgrade Path

React 16 → 17 → 18

Breaking Changes by Version:

React 17:

Event delegation changes
No event pooling
Effect cleanup timing
JSX transform (no React import needed)

React 18:

Automatic batching
Concurrent rendering
Strict Mode changes (double invocation)
New root API
Suspense on server

Class to Hooks Migration

State Management

// Before: Class component
class Counter extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0,
      name: "",
    };
  }

  increment = () => {
    this.setState({ count: this.state.count + 1 });
  };

  render() {
    return (
      <div>
        <p>Count: {this.state.count}</p>
        <button onClick={this.increment}>Increment</button>
      </div>
    );
  }
}

// After: Functional component with hooks
function Counter() {
  const [count, setCount] = useState(0);
  const [name, setName] = useState("");

  const increment = () => {
    setCount(count + 1);
  };

  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={increment}>Increment</button>
    </div>
  );
}

Lifecycle Methods to Hooks

// Before: Lifecycle methods
class DataFetcher extends React.Component {
  state = { data: null, loading: true };

  componentDidMount() {
    this.fetchData();
  }

  componentDidUpdate(prevProps) {
    if (prevProps.id !== this.props.id) {
      this.fetchData();
    }
  }

  componentWillUnmount() {
    this.cancelRequest();
  }

  fetchData = async () => {
    const data = await fetch(`/api/${this.props.id}`);
    this.setState({ data, loading: false });
  };

  cancelRequest = () => {
    // Cleanup
  };

  render() {
    if (this.state.loading) return <div>Loading...</div>;
    return <div>{this.state.data}</div>;
  }
}

// After: useEffect hook
function DataFetcher({ id }) {
  const [data, setData] = useState(null);
  const [loading, setLoading] = useState(true);

  useEffect(() => {
    let cancelled = false;

    const fetchData = async () => {
      try {
        const response = await fetch(`/api/${id}`);
        const result = await response.json();

        if (!cancelled) {
          setData(result);
          setLoading(false);
        }
      } catch (error) {
        if (!cancelled) {
          console.error(error);
        }
      }
    };

    fetchData();

    // Cleanup function
    return () => {
      cancelled = true;
    };
  }, [id]); // Re-run when id changes

  if (loading) return <div>Loading...</div>;
  return <div>{data}</div>;
}

Context and HOCs to Hooks

// Before: Context consumer and HOC
const ThemeContext = React.createContext();

class ThemedButton extends React.Component {
  static contextType = ThemeContext;

  render() {
    return (
      <button style={{ background: this.context.theme }}>
        {this.props.children}
      </button>
    );
  }
}

// After: useContext hook
function ThemedButton({ children }) {
  const { theme } = useContext(ThemeContext);

  return <button style={{ background: theme }}>{children}</button>;
}

// Before: HOC for data fetching
function withUser(Component) {
  return class extends React.Component {
    state = { user: null };

    componentDidMount() {
      fetchUser().then((user) => this.setState({ user }));
    }

    render() {
      return <Component {...this.props} user={this.state.user} />;
    }
  };
}

// After: Custom hook
function useUser() {
  const [user, setUser] = useState(null);

  useEffect(() => {
    fetchUser().then(setUser);
  }, []);

  return user;
}

function UserProfile() {
  const user = useUser();
  if (!user) return <div>Loading...</div>;
  return <div>{user.name}</div>;
}

React 18 Concurrent Features

New Root API

// Before: React 17
import ReactDOM from "react-dom";

ReactDOM.render(<App />, document.getElementById("root"));

// After: React 18
import { createRoot } from "react-dom/client";

const root = createRoot(document.getElementById("root"));
root.render(<App />);

Automatic Batching

// React 18: All updates are batched
function handleClick() {
  setCount((c) => c + 1);
  setFlag((f) => !f);
  // Only one re-render (batched)
}

// Even in async:
setTimeout(() => {
  setCount((c) => c + 1);
  setFlag((f) => !f);
  // Still batched in React 18!
}, 1000);

// Opt out if needed
import { flushSync } from "react-dom";

flushSync(() => {
  setCount((c) => c + 1);
});
// Re-render happens here
setFlag((f) => !f);
// Another re-render

Transitions

import { useState, useTransition } from "react";

function SearchResults() {
  const [query, setQuery] = useState("");
  const [results, setResults] = useState([]);
  const [isPending, startTransition] = useTransition();

  const handleChange = (e) => {
    // Urgent: Update input immediately
    setQuery(e.target.value);

    // Non-urgent: Update results (can be interrupted)
    startTransition(() => {
      setResults(searchResults(e.target.value));
    });
  };

  return (
    <>
      <input value={query} onChange={handleChange} />
      {isPending && <Spinner />}
      <Results data={results} />
    </>
  );
}

Suspense for Data Fetching

import { Suspense } from "react";

// Resource-based data fetching (with React 18)
const resource = fetchProfileData();

function ProfilePage() {
  return (
    <Suspense fallback={<Loading />}>
      <ProfileDetails />
      <Suspense fallback={<Loading />}>
        <ProfileTimeline />
      </Suspense>
    </Suspense>
  );
}

function ProfileDetails() {
  // This will suspend if data not ready
  const user = resource.user.read();
  return <h1>{user.name}</h1>;
}

function ProfileTimeline() {
  const posts = resource.posts.read();
  return <Timeline posts={posts} />;
}

Additional patterns and templates

More detailed templates and worked examples live in references/details.md. Read that file for the full pattern library.

Other skills for the same job

different authors, same section of the catalogue

MCP Builder

by anthropics

vendor ×13

Guide for creating high-quality MCP (Model Context Protocol) servers that enable LLMs to interact with external services through well-designed tools. Use when building MCP servers to integrate external APIs or services, whether in Python (FastMCP) or Node/TypeScript (MCP SDK).

Automatically creates user-facing changelogs from git commits by analyzing commit history, categorizing changes, and transforming technical commits into clear, customer-friendly release notes. Turns hours of manual changelog writing into minutes of automated generation.

774 tokens

Finishing A Development Branch

by ZhanlinCui

×7

Use when implementation is complete, all tests pass, and you need to decide how to integrate the work - guides completion of development work by presenting structured options for merge, PR, or cleanup

Vercel React Native Skills

by vercel-labs

vendor ×6

React Native and Expo best practices for building performant mobile apps. Use when building React Native components, optimizing list performance, implementing animations, or working with native modules. Triggers on tasks involving React Native, Expo, mobile performance, or native platform APIs.

39k tokens

Vercel React Best Practices

by ratacat

×5

React and Next.js performance optimization guidelines from Vercel Engineering. This skill should be used when writing, reviewing, or refactoring React/Next.js code to ensure optimal performance patterns. Triggers on tasks involving React components, Next.js pages, data fetching, bundle optimization, or performance improvements.

Next.js best practices - file conventions, RSC boundaries, data patterns, async APIs, metadata, error handling, route handlers, image/font optimization, bundling

Use when starting feature work that needs isolation from current workspace or before executing implementation plans - creates isolated git worktrees with smart directory selection and safety verification

1k tokens

How to use it

Copy the folder

Take wshobson/react-modernization from the repository into ~/.claude/skills for personal use, or into .claude/skills inside a project.

Check the name does not clash

The agent identifies a skill by the name field in its header. Two skills with the same name cannot sit side by side — one of them will be ignored.