Otimização de Performance Web

Guia Detalhado

Leia o guia detalhado antes de executar esta habilidade. Ele contém o procedimento completo e material de referência. Considere seus requisitos de segurança, pré-requisitos e validação como obrigatórios. Para um trabalho focado, carregue as seções relevantes; para um trabalho de ponta a ponta, leia o guia completamente.

Quando Usar Esta Habilidade

• Use quando o site ou aplicativo estiver carregando lentamente
• Use ao otimizar para Core Web Vitals (LCP, INP, CLS)
• Use ao reduzir o tamanho do pacote JavaScript
• Use ao reduzir o bloqueio da thread principal e interações lentas (INP)
• Use ao otimizar imagens e assets
• Use ao implementar estratégias de cache
• Use ao depurar gargalos de performance
• Use ao se preparar para auditorias de performance

Exemplos

Exemplo 1: Otimizando Core Web Vitals

## Performance Audit Results

### Current Metrics (Before Optimization)
- **LCP (Largest Contentful Paint):** 4.2s ❌ (should be < 2.5s)
- **INP (Interaction to Next Paint):** 350ms ❌ (should be ≤ 200ms)
- **CLS (Cumulative Layout Shift):** 0.25 ❌ (should be < 0.1)
- **Lighthouse Score:** 62/100

### Issues Identified

1. **LCP Issue:** Hero image (2.5MB) loads slowly
2. **INP Issue:** Large JavaScript bundle (850KB) blocks main thread
3. **CLS Issue:** Images without dimensions cause layout shifts

### Optimization Plan

#### Fix LCP (Largest Contentful Paint)

**Problem:** Hero image is 2.5MB and loads slowly

**Solutions:**
\`\`\`html
<!-- Before: Unoptimized image -->
<img src="/hero.jpg" alt="Hero">

<!-- After: Optimized with modern formats -->
<picture>
  <source srcset="/hero.avif" type="image/avif">
  <source srcset="/hero.webp" type="image/webp">
  <img 
    src="/hero.jpg" 
    alt="Hero"
    width="1200" 
    height="600"
    loading="eager"
    fetchpriority="high"
  >
</picture>
\`\`\`

**Additional optimizations:**
- Compress image to < 200KB
- Use CDN for faster delivery
- Preload hero image: `<link rel="preload" as="image" href="/hero.avif">`

#### Fix INP (Interaction to Next Paint)

**Problem:** 850KB JavaScript bundle blocks main thread

**Solutions:**

1. **Code Splitting:**
\`\`\`javascript
// Before: Everything in one bundle
import { HeavyComponent } from './HeavyComponent';
import { Analytics } from './analytics';
import { ChatWidget } from './chat';

// After: Lazy load non-critical code
const HeavyComponent = lazy(() => import('./HeavyComponent'));
const ChatWidget = lazy(() => import('./chat'));

// Load analytics after page interactive
if (typeof window !== 'undefined') {
  window.addEventListener('load', () => {
    import('./analytics').then(({ Analytics }) => {
      Analytics.init();
    });
  });
}
\`\`\`

2. **Remove Unused Dependencies:**
\`\`\`bash
# Analyze bundle
npx webpack-bundle-analyzer

# Remove unused packages
npm uninstall moment  # Use date-fns instead (smaller)
npm install date-fns
\`\`\`

3. **Defer Non-Critical Scripts:**
\`\`\`html
<!-- Before: Blocks rendering -->
<script src="/analytics.js"></script>

<!-- After: Deferred -->
<script src="/analytics.js" defer></script>
\`\`\`

#### Fix CLS (Cumulative Layout Shift)

**Problem:** Images without dimensions cause layout shifts

**Solutions:**
\`\`\`html
<!-- Before: No dimensions -->
<img src="/product.jpg" alt="Product">

<!-- After: With dimensions -->
<img 
  src="/product.jpg" 
  alt="Product"
  width="400" 
  height="300"
  style="aspect-ratio: 4/3;"
>
\`\`\`

**For dynamic content:**
\`\`\`css
/* Reserve space for content that loads later */
.skeleton-loader {
  min-height: 200px;
  background: linear-gradient(90deg, #f0f0f0 25%, #e0e0e0 50%, #f0f0f0 75%);
  background-size: 200% 100%;
  animation: loading 1.5s infinite;
}

@keyframes loading {
  0% { background-position: 200% 0; }
  100% { background-position: -200% 0; }
}
\`\`\`

### Results After Optimization

- **LCP:** 1.8s ✅ (improved by 57%)
- **INP:** 150ms ✅ (improved by 57%)
- **CLS:** 0.05 ✅ (improved by 80%)
- **Lighthouse Score:** 94/100 ✅

Exemplo 2: Reduzindo o Tamanho do Pacote JavaScript

## Otimização do Tamanho do Pacote

### Estado Atual
- **Pacote Total:** 850KB (com gzip: 280KB)
- **Pacote Principal:** 650KB
- **Pacote de Fornecedores:** 200KB
- **Tempo de Carregamento (3G):** 8.2s

### Análise

\`\`\`bash
# Analisar composição do pacote
npx webpack-bundle-analyzer dist/stats.json
\`\`\`

**Achados:**
1. Moment.js: 67KB (pode ser substituído por date-fns: 12KB)
2. Lodash: 72KB (usando a biblioteca inteira, precisa apenas de 5 funções)

…