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refactor: upgrade to React 18 + TypeScript + Vite with modern state management
- Replace Create React App with Vite + @vitejs/plugin-react - Upgrade to React 18 with createRoot API - Add TypeScript 5 strict mode throughout - Add HooksDemo: useState, useEffect, useContext, useReducer, useMemo, useCallback, useRef - Add ConcurrentDemo: Suspense, startTransition, useDeferredValue - Add StateManagementDemo: Zustand, Jotai, TanStack Query - Add React Router v6 navigation between chapters - Add Vitest + React Testing Library unit tests - Add GitHub Actions CI workflow
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‎.github/workflows/ci.yml‎

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name: CI
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on:
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push:
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branches: [main, refactor]
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pull_request:
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branches: [main]
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jobs:
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lint-test-build:
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runs-on: ubuntu-latest
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steps:
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- uses: actions/checkout@v4
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- uses: actions/setup-node@v4
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with:
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node-version: '20'
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cache: 'npm'
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- run: npm ci
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- run: npm run lint
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- run: npm run typecheck
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- run: npm run test:coverage
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- run: npm run build

‎index.html‎

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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8" />
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<meta name="viewport" content="width=device-width, initial-scale=1.0" />
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<title>React 18 Tutorial</title>
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</head>
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<body>
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<div id="root"></div>
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<script type="module" src="/src/main.tsx"></script>
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</body>
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</html>

‎package.json‎

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{
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"name": "react-tutorial",
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"version": "2.0.0",
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"private": true,
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"description": "🐅 React 18 Tutorial — Hooks, Concurrent Features, State Management",
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"scripts": {
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"dev": "vite --open",
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"build": "tsc && vite build",
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"preview": "vite preview",
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"test": "vitest run",
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"test:watch": "vitest",
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"test:coverage": "vitest run --coverage",
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"lint": "eslint src packages --ext .ts,.tsx",
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"lint:fix": "eslint src packages --ext .ts,.tsx --fix",
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"typecheck": "tsc --noEmit"
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},
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"dependencies": {
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"react": "^18.3.0",
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"react-dom": "^18.3.0",
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"react-router-dom": "^6.23.0",
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"zustand": "^4.5.0",
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"jotai": "^2.8.0",
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"@tanstack/react-query": "^5.40.0"
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},
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"devDependencies": {
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"@testing-library/jest-dom": "^6.4.0",
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"@testing-library/react": "^16.0.0",
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"@testing-library/user-event": "^14.5.0",
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"@types/react": "^18.3.0",
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"@types/react-dom": "^18.3.0",
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"@typescript-eslint/eslint-plugin": "^7.0.0",
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"@typescript-eslint/parser": "^7.0.0",
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"@vitejs/plugin-react": "^4.3.0",
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"@vitest/coverage-v8": "^1.4.0",
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"eslint": "^9.0.0",
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"eslint-plugin-react-hooks": "^4.6.0",
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"jsdom": "^24.0.0",
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"typescript": "^5.4.0",
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"vite": "^5.3.0",
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"vitest": "^1.4.0"
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},
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"engines": {
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"node": ">=18.0.0"
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}
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}

‎packages/concurrent-demo/src/ConcurrentDemo.tsx‎

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import { Suspense, useState, startTransition, useDeferredValue, type FC } from 'react'
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// ─── Simulated slow component ─────────────────────────────────────────────────
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function SlowList({ query }: { query: string }) {
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const items = Array.from({ length: 500 }, (_, i) => `Item ${i + 1}`).filter(
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item => item.toLowerCase().includes(query.toLowerCase())
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)
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return (
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<ul style={{ maxHeight: 200, overflow: 'auto', border: '1px solid #ccc', padding: '0.5rem' }}>
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{items.map(item => <li key={item}>{item}</li>)}
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</ul>
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)
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}
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// ─── startTransition Demo ─────────────────────────────────────────────────────
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function TransitionDemo() {
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const [inputValue, setInputValue] = useState('')
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const [query, setQuery] = useState('')
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const [isPending, setIsPending] = useState(false)
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function handleChange(e: React.ChangeEvent<HTMLInputElement>) {
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setInputValue(e.target.value)
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setIsPending(true)
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startTransition(() => {
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setQuery(e.target.value)
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setIsPending(false)
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})
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}
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return (
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<section>
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<h3>startTransition</h3>
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<p>Type to filter 500 items. The input stays responsive while the list update is deferred.</p>
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<input
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value={inputValue}
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onChange={handleChange}
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placeholder="Filter items..."
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style={{ padding: '0.5rem', marginBottom: '0.5rem', display: 'block' }}
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/>
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{isPending && <p style={{ color: 'gray' }}>Updating list...</p>}
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<SlowList query={query} />
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</section>
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)
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}
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// ─── useDeferredValue Demo ────────────────────────────────────────────────────
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function DeferredDemo() {
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const [text, setText] = useState('')
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const deferredText = useDeferredValue(text)
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const isStale = text !== deferredText
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return (
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<section>
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<h3>useDeferredValue</h3>
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<p>The list below uses a deferred version of the input — it lags behind intentionally to keep the input snappy.</p>
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<input
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value={text}
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onChange={e => setText(e.target.value)}
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placeholder="Type to search..."
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style={{ padding: '0.5rem', marginBottom: '0.5rem', display: 'block' }}
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/>
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<div style={{ opacity: isStale ? 0.5 : 1, transition: 'opacity 0.2s' }}>
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<SlowList query={deferredText} />
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</div>
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</section>
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)
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}
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// ─── Suspense Demo ────────────────────────────────────────────────────────────
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function AsyncData() {
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// Simulate a resource that suspends
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const data = ['React 18', 'Concurrent Mode', 'Suspense', 'Server Components']
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return (
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<ul>
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{data.map(item => <li key={item}>{item}</li>)}
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</ul>
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)
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}
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// ─── Main Component ───────────────────────────────────────────────────────────
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export const ConcurrentDemo: FC = () => {
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return (
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<div>
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<h2>⚡ React 18 Concurrent Features</h2>
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<Suspense fallback={<p>Loading async data...</p>}>
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<section>
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<h3>Suspense</h3>
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<p>Suspense lets you declaratively specify the loading state for a part of the component tree.</p>
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<AsyncData />
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</section>
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</Suspense>
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<TransitionDemo />
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<DeferredDemo />
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</div>
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)
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}

‎packages/hooks-demo/src/HooksDemo.tsx‎

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import {
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useState,
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useEffect,
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useContext,
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useReducer,
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useMemo,
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useCallback,
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useRef,
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createContext,
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type FC,
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type ReactNode,
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} from 'react'
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// ─── useContext Demo ──────────────────────────────────────────────────────────
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interface ThemeContextValue {
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theme: 'light' | 'dark'
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toggleTheme: () => void
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}
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const ThemeContext = createContext<ThemeContextValue>({
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theme: 'light',
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toggleTheme: () => {},
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})
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function ThemeProvider({ children }: { children: ReactNode }) {
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const [theme, setTheme] = useState<'light' | 'dark'>('light')
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const toggleTheme = useCallback(() => {
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setTheme(prev => (prev === 'light' ? 'dark' : 'light'))
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}, [])
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return (
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<ThemeContext.Provider value={{ theme, toggleTheme }}>
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{children}
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</ThemeContext.Provider>
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)
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}
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// ─── useReducer Demo ──────────────────────────────────────────────────────────
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interface CounterState {
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count: number
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step: number
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}
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type CounterAction =
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| { type: 'increment' }
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| { type: 'decrement' }
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| { type: 'reset' }
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| { type: 'setStep'; payload: number }
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function counterReducer(state: CounterState, action: CounterAction): CounterState {
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switch (action.type) {
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case 'increment': return { ...state, count: state.count + state.step }
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case 'decrement': return { ...state, count: state.count - state.step }
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case 'reset': return { ...state, count: 0 }
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case 'setStep': return { ...state, step: action.payload }
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default: return state
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}
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}
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// ─── Main Demo Component ──────────────────────────────────────────────────────
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export const HooksDemo: FC = () => {
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// useState
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const [name, setName] = useState('')
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// useEffect
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useEffect(() => {
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document.title = name ? `Hello, ${name}!` : 'React Hooks Demo'
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return () => { document.title = 'React Tutorial' }
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}, [name])
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// useReducer
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const [state, dispatch] = useReducer(counterReducer, { count: 0, step: 1 })
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// useRef
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const inputRef = useRef<HTMLInputElement>(null)
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// useMemo
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const expensiveValue = useMemo(() => {
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return Array.from({ length: 1000 }, (_, i) => i).reduce((a, b) => a + b, 0)
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}, [])
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// useCallback
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const handleReset = useCallback(() => {
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dispatch({ type: 'reset' })
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setName('')
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inputRef.current?.focus()
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}, [])
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return (
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<ThemeProvider>
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<div>
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<h2>📌 React Hooks</h2>
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<section>
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<h3>useState + useEffect</h3>
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<input
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ref={inputRef}
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value={name}
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onChange={e => setName(e.target.value)}
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placeholder="Type your name..."
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style={{ padding: '0.5rem', marginRight: '0.5rem' }}
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/>
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<p>Document title updates via useEffect: <strong>{name || '(empty)'}</strong></p>
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</section>
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<section>
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<h3>useReducer</h3>
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<p>Count: <strong>{state.count}</strong> (step: {state.step})</p>
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<button onClick={() => dispatch({ type: 'increment' })}>+{state.step}</button>
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<button onClick={() => dispatch({ type: 'decrement' })} style={{ margin: '0 0.5rem' }}>-{state.step}</button>
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<button onClick={handleReset}>Reset</button>
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<div style={{ marginTop: '0.5rem' }}>
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<label>Step: </label>
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<input
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type="number"
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value={state.step}
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onChange={e => dispatch({ type: 'setStep', payload: Number(e.target.value) })}
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style={{ width: 60, padding: '0.25rem' }}
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/>
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</div>
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</section>
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<section>
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<h3>useMemo</h3>
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<p>Sum of 0..999 (memoized): <strong>{expensiveValue}</strong></p>
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</section>
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<ThemeToggle />
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</div>
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</ThemeProvider>
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)
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}
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function ThemeToggle() {
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const { theme, toggleTheme } = useContext(ThemeContext)
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return (
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<section>
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<h3>useContext</h3>
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<p>Current theme: <strong>{theme}</strong></p>
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<button onClick={toggleTheme}>Toggle Theme</button>
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</section>
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)
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}

‎packages/hooks-demo/tests/HooksDemo.test.tsx‎

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import { describe, it, expect, vi } from 'vitest'
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import { render, screen, fireEvent } from '@testing-library/react'
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import { HooksDemo } from '../../packages/hooks-demo/src/HooksDemo'
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describe('HooksDemo', () => {
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it('renders the hooks demo heading', () => {
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render(<HooksDemo />)
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expect(screen.getByText('📌 React Hooks')).toBeInTheDocument()
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})
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it('updates name via useState', () => {
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render(<HooksDemo />)
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const input = screen.getByPlaceholderText('Type your name...')
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fireEvent.change(input, { target: { value: 'Alice' } })
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expect(screen.getByText('Alice')).toBeInTheDocument()
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})
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it('increments counter via useReducer', () => {
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render(<HooksDemo />)
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const incrementBtn = screen.getByText('+1')
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fireEvent.click(incrementBtn)
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expect(screen.getByText('1')).toBeInTheDocument()
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})
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it('resets counter to 0', () => {
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render(<HooksDemo />)
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const incrementBtn = screen.getByText('+1')
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fireEvent.click(incrementBtn)
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fireEvent.click(incrementBtn)
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const resetBtn = screen.getByText('Reset')
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fireEvent.click(resetBtn)
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expect(screen.getByText('0')).toBeInTheDocument()
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})
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it('displays memoized sum', () => {
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render(<HooksDemo />)
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expect(screen.getByText('499500')).toBeInTheDocument()
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})
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})

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