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.
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Master React version upgrades, class to hooks migration, concurrent features adoption, and codemods for automated transformation.
Breaking Changes by Version:
React 17:
React 18:
// 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>
);
}
// 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>;
}
// 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>;
}
// 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 />);
// 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
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} />
</>
);
}
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} />;
}
More detailed templates and worked examples live in references/details.md. Read that file for the full pattern library.
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Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
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Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
Set up and use 1Password CLI (op). Use when installing the CLI, enabling desktop app integration, signing in (single or multi-account), or reading/injecting/running secrets via op.
CLI to manage emails via IMAP/SMTP. Use `himalaya` to list, read, write, reply, forward, search, and organize emails from the terminal. Supports multiple accounts and message composition with MML (MIME Meta Language).