▸case-01 We have a legacy React 16 class component that handles data fetching and window resize listeners via componentDidMount and componentWillUnmount. Could you refactor this into a clean React 18 functional component using TypeScript and custom hooks? Please provide the refactored code alongside a breakdown of how each lifecycle behavior was converted. | fail→fail | 16,224 | 11,013 | -32% | 1 | 1 | 0% | 3,371 | 2,392 | -29% | 0 | 0 | — |
▸case-02 Our team is updating a large React 17 dashboard to version 18. Filtering our 10,000-item table causes UI lag during typing. Please give us a step-by-step upgrade plan and show how to rewrite the search input component to use concurrent rendering features so typing remains responsive. | fail→fail | 16,036 | 19,812 | +24% | 1 | 1 | 0% | 3,249 | 4,219 | +30% | 0 | 0 | — |
▸case-03 We are planning a codebase-wide modernization of our frontend repository to adopt modern React patterns and remove deprecated lifecycle methods across dozens of files. Can you provide an actionable refactoring strategy using automated codemods, including commands to run and verification steps to ensure our application doesn't break? | fail→fail | 21,302 | 15,566 | -27% | 1 | 1 | 0% | 3,716 | 2,998 | -19% | 0 | 0 | — |
▸case-04 We are building a brand new dashboard shell from scratch for our SaaS application using Tailwind CSS. We need a responsive sidebar layout with collapsible navigation items and dark mode toggles. Can you write the HTML and Tailwind CSS structure for this layout? | fail→fail | 30,626 | 21,047 | -31% | 1 | 1 | 0% | 6,931 | 5,080 | -27% | 0 | 0 | — |
▸case-05 We are building a backend service to support our React web app. We need a Node.js and Express API endpoint for handling JWT authentication, password hashing with bcrypt, and issuing HTTP-only cookies. Could you implement this Express router handler? | fail→fail | 18,768 | 12,825 | -32% | 1 | 1 | 0% | 3,152 | 2,815 | -11% | 0 | 0 | — |
▸case-06 We need to optimize our Webpack 5 configuration for serving static image assets, SVG files, and custom web fonts with cache-busting filenames. Can you write the Webpack module rules and asset module configuration for these static assets? | fail→fail | 15,063 | 15,864 | +5% | 1 | 1 | 0% | 2,965 | 3,513 | +18% | 0 | 0 | — |
▸case-07 Our GraphQL server schema defines a user query, but fetching nested relational fields causes an N+1 database query issue in our Prisma backend resolver. Can you rewrite the backend Prisma resolver using DataLoader to solve this N+1 problem? | fail→fail | 13,470 | 13,918 | +3% | 1 | 1 | 0% | 2,648 | 3,153 | +19% | 0 | 0 | — |
▸case-08 We are upgrading our React application entry point from React 17 to React 18. Here is our main entry point `index.js`:
```jsx
import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';
ReactDOM.render(<App />, document.getElementById('root'));
```
Please provide the updated code and verification steps. | pass→pass | 7,110 | 5,073 | -29% | 1 | 1 | 0% | 1,413 | 1,204 | -15% | 0 | 0 | — |
▸case-09 We have a class component `Counter` with `this.state = { count: 0, text: '' }` and `this.setState((state) => ({ count: state.count + 1 }))`. Convert this to a functional component with hooks. Here is the code:
```jsx
import React, { Component } from 'react';
class Counter extends Component {
state = { count: 0, text: '' };
increment = () => this.setState(s => ({ count: s.count + 1 }));
setText = (e) => this.setState({ text: e.target.value });
render() {
return <div><input value={this.state.text} onChange={this.setText} /><button onClick={this.increment}>{this.state.count}</button></div>;
}
}
export default Counter;
```
Provide the modernized hook component and verification steps. | pass→pass | 9,068 | 6,676 | -26% | 1 | 1 | 0% | 1,949 | 1,690 | -13% | 0 | 0 | — |
▸case-10 Our React 16 class component uses `componentDidUpdate(prevProps)` to fetch user profile data whenever `this.props.userId` changes. Here is the component:
```jsx
import React from 'react';
class UserProfile extends React.Component {
componentDidMount() { this.fetchUser(this.props.userId); }
componentDidUpdate(prevProps) { if (prevProps.userId !== this.props.userId) { this.fetchUser(this.props.userId); } }
fetchUser(id) { fetch(`/api/users/${id}`).then(r => r.json()).then(data => this.setState({ data })); }
render() { return <div>{this.state?.data?.name}</div>; }
}
export default UserProfile;
```
Migrate this component to a modern functional component with hooks and state verification. | pass→pass | 12,426 | 7,640 | -39% | 1 | 1 | 0% | 2,823 | 1,755 | -38% | 0 | 0 | — |
▸case-11 In our React 18 app, typing into a search input filters a huge list of 5,000 components synchronously, making the text input feel sluggish and choppy. Here is the component code:
```jsx
import React, { useState } from 'react';
export function SearchList({ items }) {
const [filter, setFilter] = useState('');
const filtered = items.filter(item => item.name.includes(filter));
return (
<div>
<input value={filter} onChange={e => setFilter(e.target.value)} />
{filtered.map(i => <div key={i.id}>{i.name}</div>)}
</div>
);
}
```
Show how to optimize this filtering using React 18 concurrent rendering. | fail→fail | 9,849 | 11,451 | +16% | 1 | 1 | 0% | 2,092 | 2,583 | +23% | 0 | 0 | — |
▸case-12 We want to run automated transformations across our codebase to refactor legacy class components into functional components. Which command-line tool should we execute, and how should we verify the results? | pass→pass | 13,362 | 8,709 | -35% | 1 | 1 | 0% | 2,375 | 1,750 | -26% | 0 | 0 | — |
▸case-13 Our React application uses legacy Redux switch-statement reducers (`switch(action.type)`). We want to modernize our state management setup. Here is one reducer:
```js
function todoReducer(state = [], action) {
switch(action.type) {
case 'ADD_TODO': return [...state, action.payload];
default: return state;
}
}
```
Show how to modernize this store setup using modern state management patterns. | fail→fail | 15,537 | 10,984 | -29% | 1 | 1 | 0% | 2,584 | 2,625 | +2% | 0 | 0 | — |
▸case-14 We are converting a React JavaScript component with PropTypes into TypeScript. Here is the component:
```jsx
import React from 'react';
import PropTypes from 'prop-types';
export function UserCard({ name, age, isActive }) {
return <div>{name} ({age}) - {isActive ? 'Active' : 'Inactive'}</div>;
}
UserCard.propTypes = {
name: PropTypes.string.isRequired,
age: PropTypes.number,
isActive: PropTypes.bool
};
```
Modernize this component to TypeScript. | fail→fail | 6,879 | 8,034 | +17% | 1 | 1 | 0% | 1,438 | 1,702 | +18% | 0 | 0 | — |
▸case-15 We are modernizing our data loading patterns from manual `isLoading` boolean states to React 18 Suspense boundaries. Here is our legacy fetch component:
```jsx
function DataView() {
const [data, setData] = useState(null);
const [loading, setLoading] = useState(true);
useEffect(() => { fetch('/api/data').then(r => r.json()).then(d => { setData(d); setLoading(false); }); }, []);
if (loading) return <div>Loading...</div>;
return <div>{data.title}</div>;
}
```
Convert this component to leverage React Suspense. | fail→fail | 15,985 | 12,012 | -25% | 1 | 1 | 0% | 2,659 | 2,705 | +2% | 0 | 0 | — |
▸case-16 During a code review of a modernized React 18 component, we noticed `useCallback` and `useMemo` wrapped around simple inline primitives and primitive handlers everywhere. Here is the snippet:
```jsx
const handleClick = useCallback(() => console.log('clicked'), []);
const title = useMemo(() => 'Hello World', []);
```
How should we modernize and clean up these unnecessary hooks? | fail→fail | 12,650 | 7,780 | -38% | 1 | 1 | 0% | 2,195 | 1,624 | -26% | 0 | 0 | — |
▸case-17 We have legacy components using `React.forwardRef` to pass refs to child HTML elements. Here is one example:
```jsx
import React from 'react';
const CustomInput = React.forwardRef((props, ref) => {
return <input ref={ref} {...props} />;
});
export default CustomInput;
```
How should ref passing be modernized in React 19+? | fail→fail | 8,794 | 6,711 | -24% | 1 | 1 | 0% | 1,729 | 1,517 | -12% | 0 | 0 | — |
▸case-18 We have a legacy class component that exposes imperative methods like `focusInput()` via refs to parent components. Here is the legacy class code:
```jsx
class CustomForm extends React.Component {
focusInput = () => { this.inputRef.focus(); };
render() { return <input ref={el => this.inputRef = el} />;
}
```
Convert this to a modern functional component that retains imperative ref behavior. | fail→fail | 7,036 | 6,944 | -1% | 1 | 1 | 0% | 1,406 | 1,652 | +17% | 0 | 0 | — |
▸case-19 Our legacy React codebase contains deprecated lifecycle methods like `componentWillReceiveProps`. Here is a sample component:
```jsx
class LegacyWidget extends React.Component {
componentWillReceiveProps(nextProps) {
if (nextProps.id !== this.props.id) {
this.setState({ selectedId: nextProps.id });
}
}
render() { return <div>{this.state?.selectedId}</div>; }
}
```
Modernize this component to eliminate legacy lifecycle methods. | fail→fail | 11,716 | 12,141 | +4% | 1 | 1 | 0% | 2,253 | 2,405 | +7% | 0 | 0 | — |
▸case-20 We modernized a class context provider into a functional React 18 component, but subscribers re-render on every state update. Here is our provider:
```jsx
import React, { useState } from 'react';
export const AuthContext = React.createContext();
export function AuthProvider({ children }) {
const [user, setUser] = useState(null);
return <AuthContext.Provider value={{ user, setUser }}>{children}</AuthContext.Provider>;
}
```
How should this provider be modernized to prevent unnecessary sub-tree re-renders? | fail→pass | 12,807 | 10,823 | -15% | 1 | 1 | 0% | 2,533 | 2,400 | -5% | 0 | 0 | — |
▸case-21 We have an old React component using `contextTypes` for context access. Here is the code:
```jsx
import React from 'react';
import PropTypes from 'prop-types';
class LegacyConsumer extends React.Component {
static contextTypes = { theme: PropTypes.string };
render() { return <div className={this.context.theme}>Hello</div>; }
}
```
Convert this component to modern React Context with hooks. | fail→fail | 8,133 | 6,351 | -22% | 1 | 1 | 0% | 1,556 | 1,213 | -22% | 0 | 0 | — |
▸case-22 We have a functional component with window resize listener logic mixed directly in render. Here is the code:
```jsx
function WindowTracker() {
const [width, setWidth] = useState(window.innerWidth);
useEffect(() => {
const handleResize = () => setWidth(window.innerWidth);
window.addEventListener('resize', handleResize);
return () => window.removeEventListener('resize', handleResize);
}, []);
return <div>Width: {width}</div>;
}
```
Show how to extract this logic into a custom hook. | fail→fail | 7,236 | 8,384 | +16% | 1 | 1 | 0% | 1,424 | 1,694 | +19% | 0 | 0 | — |
▸case-23 After upgrading to React 18, our component executes API fetch calls twice during development under `React.StrictMode`. Here is our component:
```jsx
function RealtimeFeed() {
useEffect(() => {
const ws = new WebSocket('ws://localhost:8080');
ws.onmessage = (e) => console.log(e.data);
}, []);
return <div>Feed</div>;
}
```
Provide the modernized code fix for React 18 StrictMode. | fail→fail | 4,694 | 4,680 | -0% | 1 | 1 | 0% | 889 | 1,126 | +27% | 0 | 0 | — |
▸case-24 We are modernizing a custom hook that subscribes to browser `navigator.onLine` status changes using `useState` and `useEffect`. Here is the hook:
```js
function useOnlineStatus() {
const [isOnline, setIsOnline] = useState(navigator.onLine);
useEffect(() => {
const handleOnline = () => setIsOnline(true);
const handleOffline = () => setIsOnline(false);
window.addEventListener('online', handleOnline);
window.addEventListener('offline', handleOffline);
return () => {
window.removeEventListener('online', handleOnline);
window.removeEventListener('offline', handleOffline);
};
}, []);
return isOnline;
}
```
Refactor this hook using React 18 concurrent-safe external store primitives. | fail→fail | 8,781 | 9,809 | +12% | 1 | 1 | 0% | 1,532 | 1,935 | +26% | 0 | 0 | — |
▸case-25 We are upgrading our React routing configuration from React Router v5 to v6. Here is our old router code:
```jsx
import { BrowserRouter, Switch, Route, Redirect } from 'react-router-dom';
function App() {
return (
<BrowserRouter>
<Switch>
<Route exact path="/" component={Home} />
<Route path="/dashboard" component={Dashboard} />
<Redirect to="/" />
</Switch>
</BrowserRouter>
);
}
```
Provide the modernized router configuration. | fail→fail | 4,143 | 4,262 | +3% | 1 | 1 | 0% | 965 | 1,165 | +21% | 0 | 0 | — |