Web performance optimization

Web Performance Optimization

Overview

Implement performance optimization strategies including lazy loading, code splitting, caching, compression, and monitoring to improve Core Web Vitals and user experience.

When to Use

• Slow page load times
• High Largest Contentful Paint (LCP)
• Large bundle sizes
• Frequent Cumulative Layout Shift (CLS)
• Mobile performance issues

Code Splitting (React)

import { lazy, Suspense } from 'react';
import { Routes, Route } from 'react-router-dom';

const Home = lazy(() => import('./pages/Home'));
const Dashboard = lazy(() => import('./pages/Dashboard'));
const Settings = lazy(() => import('./pages/Settings'));

function App() {
  return (
    <Suspense fallback={<Loading />}>
      <Routes>
        <Route path="/" element={<Home />} />
        <Route path="/dashboard" element={<Dashboard />} />
        <Route path="/settings" element={<Settings />} />
      </Routes>
    </Suspense>
  );
}

Webpack Bundle Optimization

// webpack.config.js
module.exports = {
  optimization: {
    splitChunks: {
      chunks: 'all',
      cacheGroups: {
        vendor: {
          test: /[\\/]node_modules[\\/]/,
          name: 'vendors',
          chunks: 'all'
        }
      }
    }
  }
};

Image Optimization

<picture>
  <source srcset="image.webp" type="image/webp">
  <source srcset="image.jpg" type="image/jpeg">
  <img
    src="image.jpg"
    srcset="image-400.jpg 400w, image-800.jpg 800w, image-1200.jpg 1200w"
    sizes="(max-width: 600px) 100vw, 50vw"
    loading="lazy"
    decoding="async"
    alt="Description"
  >
</picture>

Service Worker Caching

// sw.js
const CACHE_NAME = 'app-v1';
const ASSETS = ['/', '/index.html', '/main.js', '/styles.css'];

self.addEventListener('install', (event) => {
  event.waitUntil(
    caches.open(CACHE_NAME).then(cache => cache.addAll(ASSETS))
  );
});

self.addEventListener('fetch', (event) => {
  event.respondWith(
    caches.match(event.request).then(cached => {
      return cached || fetch(event.request).then(response => {
        return caches.open(CACHE_NAME).then(cache => {
          cache.put(event.request, response.clone());
          return response;
        });
      });
    })
  );
});

Core Web Vitals Monitoring

// Track LCP, CLS, INP (Note: INP replaced FID as of March 2024)
// sendToAnalytics is a placeholder function that sends metrics to your analytics endpoint
// Expected signature: sendToAnalytics({ metric: string, value: number }) => void
// Example implementation:
function sendToAnalytics({ metric, value }) {
  // Replace with your analytics implementation (e.g., Google Analytics, Segment)
  fetch('/api/analytics', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ metric, value, timestamp: Date.now() })
  });
}

// Largest Contentful Paint (LCP)
new PerformanceObserver((list) => {
  for (const entry of list.getEntries()) {
    console.log(`LCP: ${entry.startTime}ms`);
    sendToAnalytics({ metric: 'LCP', value: entry.startTime });
  }
}).observe({ type: 'largest-contentful-paint', buffered: true });

// Cumulative Layout Shift (CLS)
new PerformanceObserver((list) => {
  let cls = 0;
  for (const entry of list.getEntries()) {
    if (!entry.hadRecentInput) cls += entry.value;
  }
  sendToAnalytics({ metric: 'CLS', value: cls });
}).observe({ type: 'layout-shift', buffered: true });

// Interaction to Next Paint (INP) - replaces FID
new PerformanceObserver((list) => {
  for (const entry of list.getEntries()) {
    // INP measures responsiveness - duration of slowest interaction
    const inp = entry.processingEnd - entry.processingStart;
    console.log(`INP: ${inp}ms`);
    sendToAnalytics({ metric: 'INP', value: inp });
  }
}).observe({ type: 'event', buffered: true }); // 'event' captures interaction events

Performance Targets

Metric	Good	Needs Improvement
LCP	<2.5s	2.5-4s
INP	<200ms	200-500ms
CLS	<0.1	0.1-0.25
TTI	<3.8s	3.8-7.3s

Note: INP (Interaction to Next Paint) replaced FID (First Input Delay) as a Core Web Vital in March 2024. INP provides a more comprehensive measure of page responsiveness by capturing the full duration of interactions, not just the input delay.

Compression (Nginx)

gzip on;
gzip_types text/plain text/css application/json application/javascript;
gzip_min_length 1000;
gzip_comp_level 6;

Best Practices

• Minimize bundle size with code splitting
• Optimize images with appropriate formats
• Implement lazy loading strategically
• Use HTTP caching headers
• Enable gzip/brotli compression
• Monitor Core Web Vitals continuously
• Implement service workers
• Defer non-critical JavaScript
• Optimize critical rendering path
• Test on real devices and networks

Optimization Checklist

• Enable code splitting for routes
• Lazy load below-fold components
• Optimize and compress images
• Implement service worker caching
• Enable gzip/brotli compression
• Monitor Core Web Vitals
• Minimize render-blocking resources

Additional Configuration

See references/compression-monitoring.md for:

• Webpack compression plugin setup
• Apache .htaccess compression config
• TTFB monitoring implementation
• Puppeteer automation for measurement

See references/typescript-advanced.md for:

• TypeScript lazyLoad utility
• TypeScript image component
• Advanced service worker with offline fallback
• TerserPlugin configuration
• Complete PerformanceMetrics interface

Tools

• Lighthouse / PageSpeed Insights
• WebPageTest
• Chrome DevTools Performance tab
• web-vitals npm package

Resources

• Web Vitals
• Google PageSpeed Insights
• Lighthouse
• WebPageTest
• Performance API