OrderPage
  ├── OrderHeader      （Order Number、Status）
  ├── OrderItems       （Product List）
  │   └── OrderItem    × N（Single Item，Includes price calculation）
  ├── ShippingInfo     （Shipping Information）
  └── PaymentInfo      （Payment Information）

import { Component, ErrorInfo, ReactNode } from 'react'

interface ErrorBoundaryProps {
  children: ReactNode
  /** Custom Downgrade UI */
  fallback?: ReactNode
  /** Error Callback（Submit Sentry etc.） */
  onError?: (error: Error, errorInfo: ErrorInfo) => void
}

interface ErrorBoundaryState {
  hasError: boolean
  error: Error | null
}

class ErrorBoundary extends Component<ErrorBoundaryProps, ErrorBoundaryState> {
  constructor(props: ErrorBoundaryProps) {
    super(props)
    this.state = { hasError: false, error: null }
  }

  // Static Methods：Update Based on the Error state
  static getDerivedStateFromError(error: Error): ErrorBoundaryState {
    return { hasError: true, error }
  }

  // Life Cycle：Performing side effects after catching an error（Log Reporting）
  componentDidCatch(error: Error, errorInfo: ErrorInfo) {
    console.error('ErrorBoundary An error was caught：', error.message)
    console.error('Component Stack：', errorInfo.componentStack)

    // Reported to the error monitoring service
    if (this.props.onError) {
      this.props.onError(error, errorInfo)
    }

    // Can be integrated into actual projects Sentry：
    // Sentry.captureException(error, { extra: errorInfo })
  }

  handleReset = () => {
    this.setState({ hasError: false, error: null })
  }

  render() {
    if (this.state.hasError) {
      // Use Custom fallback Or default to a lower level UI
      if (this.props.fallback) {
        return this.props.fallback
      }

      return (
        <div
          role="alert"
          style={{
            padding: '32px 24px',
            margin: 16,
            background: '#fff2f0',
            border: '1px solid #ffccc7',
            borderRadius: 8,
            textAlign: 'center',
          }}
        >
          <h2 style={{ color: '#ff4d4f', margin: '0 0 12px' }}>
            A component error occurred
          </h2>
          <p style={{ color: '#666', marginBottom: 8, fontSize: 14 }}>
            {this.state.error?.message || 'An unknown error has occurred'}
          </p>
          <button
            onClick={this.handleReset}
            style={{
              padding: '6px 20px',
              background: '#ff4d4f',
              color: '#fff',
              border: 'none',
              borderRadius: 4,
              cursor: 'pointer',
              fontSize: 14,
            }}
          >
            Retry
          </button>
        </div>
      )
    }

    return this.props.children
  }
}

export default ErrorBoundary

// Layered Wrapping — Each independent area has its own ErrorBoundary
function OrderPage({ orderId }: { orderId: string }) {
  return (
    <div>
      {/* Order Header Information：It will display correctly even if there is an error below. */}
      <ErrorBoundary fallback={<p>Failed to load order</p>}>
        <OrderHeader orderId={orderId} />
      </ErrorBoundary>

      {/* Product List：Errors in one area do not affect other areas */}
      <ErrorBoundary
        onError={(err) => {
          // Rendering Error in the List of Submitted Products
          fetch('/api/log-error', {
            method: 'POST',
            body: JSON.stringify({ error: err.message, orderId }),
          })
        }}
      >
        <OrderItems orderId={orderId} />
      </ErrorBoundary>

      {/* Payment Information */}
      <ErrorBoundary>
        <PaymentInfo orderId={orderId} />
      </ErrorBoundary>
    </div>
  )
}

import { useState } from 'react'
import ErrorBoundary from './ErrorBoundary'

// Simulating Data Retrieval That Results in Errors
function fetchUserData(userId: number) {
  return fetch(`/api/users/${userId}`).then(res => {
    if (!res.ok) throw new Error('Failed to retrieve user data')
    return res.json()
  })
}

// Data display components that may have rendering errors
function UserInfo({ userId }: { userId: number }) {
  const [user, setUser] = useState<any>(null)
  const [loading, setLoading] = useState(true)

  useState(() => {
    fetchUserData(userId)
      .then(setUser)
      .finally(() => setLoading(false))
  })

  if (loading) return <p>Loading......</p>

  // If user Data Structure Exception，An error may occur here
  return (
    <div>
      <h3>{user.name}</h3>         {/* possibly：Cannot read properties of undefined */}
      <p>{user.profile.bio}</p>    {/* possibly：Cannot read properties of undefined */}
    </div>
  )
}

// Outer Container：With retries key Mechanism
function UserProfile({ userId }: { userId: number }) {
  const [retryKey, setRetryKey] = useState(0)

  return (
    <ErrorBoundary
      key={retryKey}  // Change key It will unmount and remount the subtree
      fallback={
        <div style={{ padding: 24, textAlign: 'center' }}>
          <p>Error loading user information</p>
          <button onClick={() => setRetryKey(k => k + 1)}>
            Retry Loading
          </button>
        </div>
      }
    >
      <UserInfo userId={userId} />
    </ErrorBoundary>
  )
}

function PaymentForm() {
  async function handleSubmit() {
    try {
      const result = await submitPayment()
      // Processed successfully
    } catch (error) {
      // Asynchronous errors are caught here，Error Boundary That's none of my business
      console.error('Payment Failed：', error)
      // Display Error UI（For example, setting state）
      setError(error instanceof Error ? error.message : 'Payment Failed')
    }
  }

  // Errors in the event must also be used try/catch
  function handleClick() {
    try {
      processPayment()
    } catch (error) {
      setError('Processing Failed，Please try again.')
    }
  }
}

1. Open your browser DevTools → Components Tabs
2. Switch to Profiler Sublabel
3. Click the blue record button（Start Recording）
4. Performing actions on the page（Click、Scrolling, etc.）
5. Click the Stop button（End Recording）
6. View the flame diagram

┌────────────────────────────────────────────┐
│  App (0.3ms)                               │
│  ├── Navbar (0.2ms)                        │
│  ├── OrderPage (2.1ms)                     │
│  │   ├── OrderHeader (0.4ms)  ── Gray     │
│  │   ├── OrderItems (1.5ms)   ── Yellow     │
│  │   │   └── OrderItem × 20 (each 0.3ms)     │
│  │   └── PaymentInfo (0.2ms) ── Gray      │
│  └── Footer (0.1ms)                        │
└────────────────────────────────────────────┘

import { Profiler } from 'react'

type ProfilerPhase = 'mount' | 'update' | 'nested-update'

interface ProfileMetrics {
  id: string
  phase: ProfilerPhase
  actualDuration: number      // Actual rendering time for this render（milliseconds）
  baseDuration: number        // Worst-case runtime for a subtree
  startTime: number           // Render Start Timestamp
  commitTime: number          // Submit to DOM timestamp
  interactions: Set<any>      // Related Interaction Tracking
}

// Performance Monitoring Callbacks
function onRenderCallback(
  id: string,
  phase: ProfilerPhase,
  actualDuration: number,
  baseDuration: number,
  startTime: number,
  commitTime: number,
) {
  // Record to the performance log
  if (actualDuration > 16) {  // More than 16ms = Frame drop threshold (60fps)
    console.warn(
      `[Performance Alerts] ${id} in  ${phase} Time Taken per Stage ${actualDuration.toFixed(1)}ms，` +
      `More than 16ms Frame Budget！`
    )

    // Reported to the performance monitoring system
    // reportPerformance({ id, phase, actualDuration, baseDuration })
  }

  // Output from the development environment to the console
  if (process.env.NODE_ENV === 'development') {
    console.table({
      'Components': id,
      'Phase': phase,
      'Actual time taken(ms)': actualDuration.toFixed(1),
      'Benchmark Duration(ms)': baseDuration.toFixed(1),
    })
  }
}

// Big Data List——Potential Performance Bottlenecks
function ProductList({ products }: { products: Product[] }) {
  return (
    <Profiler id="ProductList" onRender={onRenderCallback}>
      <div style={{ display: 'grid', gap: 16, gridTemplateColumns: 'repeat(3, 1fr)' }}>
        {products.map(product => (
          <ProductCard key={product.id} product={product} />
        ))}
      </div>
    </Profiler>
  )
}

// 1. React.memo — Avoid Unnecessary Re-rendering
const ProductCard = React.memo(function ProductCard({
  product,
}: {
  product: Product
}) {
  return (
    <div style={{ border: '1px solid #eee', padding: 16, borderRadius: 8 }}>
      <img src={product.image} alt={product.name} width="100%" />
      <h4>{product.name}</h4>
      <p>${product.price}</p>
    </div>
  )
})

// 2. useMemo — Cache the results of expensive computations
function OrderSummary({ items }: { items: OrderItem[] }) {
  const totalPrice = useMemo(() => {
    return items.reduce((sum, item) => {
      // Assuming that complex currency conversions were performed here
      return sum + convertCurrency(item.price, item.currency)
    }, 0)
  }, [items])

  return <p>Total：${totalPrice.toFixed(2)}</p>
}

// 3. useCallback — Stable function references
function OrderList({ orders, onSelect }: {
  orders: Order[]
  onSelect: (id: string) => void
}) {
  // ✅ use  useCallback Keep references consistent
  const handleSelect = useCallback((id: string) => {
    onSelect(id)
  }, [onSelect])

  return orders.map(order => (
    <OrderRow key={order.id} order={order} onSelect={handleSelect} />
  ))
}

// DevTools Components Panel Examples
<OrderPage>
  <ErrorBoundary>
    <OrderHeader
      orderNumber="ORD-2026-0001"     ← Props Real-time Display
      status="shipped"                 ← Can be edited directly during testing
    />
  </ErrorBoundary>
  <ErrorBoundary>
    <OrderItems>
      <OrderItem product={...} />      ← State Expand to view
      <OrderItem product={...} />
    </OrderItems>
  </ErrorBoundary>
</OrderPage>

function useFetchWithRetry(url, maxRetries = 3) {
  const [data, setData] = useState(null)
  const [error, setError] = useState(null)
  const [loading, setLoading] = useState(true)
  const [retries, setRetries] = useState(0)

  const fetchData = useCallback(async () => {
    setLoading(true)
    setError(null)
    try {
      const res = await fetch(url)
      if (!res.ok) throw new Error(`HTTP ${res.status}`)
      const json = await res.json()
      setData(json)
    } catch (err) {
      if (retries < maxRetries) {
        setRetries(r => r + 1)
        setTimeout(fetchData, 1000 * (retries + 1))
      } else {
        setError(err.message)
      }
    } finally {
      setLoading(false)
    }
  }, [url, retries, maxRetries])

  useEffect(() => { fetchData() }, [url])

  return { data, error, loading, retries, refetch: () => { setRetries(0); fetchData() } }
}

function UserList() {
  const { data: users, error, loading, retries, refetch } = useFetchWithRetry('/api/users')

  if (loading) return <p>Loading... {retries > 0 && `(retry ${retries})`}</p>
  if (error) return (
    <div style={{ padding: 20, textAlign: 'center' }}>
      <p style={{ color: '#ff4d4f' }}>Error: {error}</p>
      <button onClick={refetch} style={{ padding: '8px 16px', cursor: 'pointer' }}>Retry</button>
    </div>
  )

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

// lib/errorReporting.ts
const SENTRY_DSN = process.env.NEXT_PUBLIC_SENTRY_DSN

function initErrorReporting() {
  if (typeof window === 'undefined') return
  if (!SENTRY_DSN) return

  // Sentry.init({ dsn: SENTRY_DSN, ... })
  // Simplified Example：Simulation Using Global Event Listeners

  window.addEventListener('unhandledrejection', (event) => {
    console.error('Unhandled Promise:', event.reason)
    reportError({
      type: 'unhandledrejection',
      message: event.reason?.message || String(event.reason),
      stack: event.reason?.stack,
      timestamp: new Date().toISOString(),
    })
  })

  window.addEventListener('error', (event) => {
    console.error('Global Error:', event.error)
    reportError({
      type: 'window.error',
      message: event.message,
      filename: event.filename,
      lineno: event.lineno,
      timestamp: new Date().toISOString(),
    })
  })
}

function reportError(payload) {
  fetch('/api/errors', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify(payload),
  }).catch(() => {})
}

// app/layout.tsx
function RootLayout({ children }) {
  useEffect(() => { initErrorReporting() }, [])
  return <html><body>{children}</body></html>
}