Web Performance Optimization

Strategies and techniques for optimizing web application performance and user experience.

Core Web Vitals

Largest Contentful Paint (LCP)

• Time to largest content element visible
• Target: < 2.5 seconds
• Optimize: image size, server response, render-blocking resources

First Input Delay (FID)

• Time for page to respond to user input
• Target: < 100 milliseconds
• Optimize: reduce JavaScript, break up tasks

Cumulative Layout Shift (CLS)

• Visual stability of page
• Target: < 0.1
• Optimize: reserve space for images/ads, avoid layout disruptions

Performance Metrics

Optimization Techniques

Image Optimization

<!-- Lazy loading -->
<img src="image.jpg" loading="lazy">

<!-- Responsive images -->
<picture>
  <source media="(max-width: 500px)" srcset="small.jpg">
  <img src="large.jpg" alt="Description">
</picture>

<!-- Modern formats -->
<picture>
  <source type="image/webp" srcset="image.webp">
  <img src="image.jpg" alt="Description">
</picture>

Code Splitting

// Dynamic import
const module = await import('./heavy-module');

// React lazy loading
const Component = React.lazy(() => import('./Component'));

Caching Strategies

• Browser cache: Set Cache-Control headers
• Service workers: Offline support and cache control
• CDN: Distribute content geographically
• Redis: Server-side caching

Minification & Compression

• Minify CSS, JavaScript, HTML
• Gzip compression
• Brotli for better compression
• Remove unused code (tree shaking)

Performance Audit Checklist

• Optimize images (format, size, lazy load)
• Minify CSS, JS, HTML
• Enable gzip/brotli compression
• Implement code splitting
• Cache static assets
• Use CDN for assets
• Optimize critical rendering path
• Remove unused dependencies
• Lazy load non-critical routes
• Optimize fonts (subset, preload)
• Implement service workers
• Monitor Core Web Vitals

Tools for Analysis

• Chrome Lighthouse - Audit performance
• WebPageTest - Detailed analysis
• Speedcurve - Continuous monitoring
• Bundle Analyzer - Webpack/Rollup bundle size
• Sentry - Error and performance monitoring

Best Practices

1. Measure First - Establish baseline metrics
2. Prioritize - Fix biggest issues first
3. Test Impact - Verify improvements
4. Monitor Continuously - Track over time
5. User-Centric - Focus on real user metrics

Example Performance Budget

JavaScript: < 200KB
CSS: < 50KB
Images: < 500KB total
Fonts: < 100KB
Total: < 850KB

References

• Web Vitals by Google
• Chrome Developers Performance
• MDN Web Performance
• Lighthouse Documentation
• WebPageTest Blog