Performance Optimization
Lighthouse Auditing
Using Google’s tool to measure and improve PWA quality:
Lighthouse Categories:
- Performance
- Accessibility
- Best Practices
- SEO
- PWA
Key PWA Audit Checks:
- Registers a service worker
- Responds with 200 when offline
- Has a web app manifest
- Redirects HTTP to HTTPS
- Loads fast on mobile networks
- Uses HTTPS
- Properly sized splash screens
- Content is sized correctly for viewport
Running Lighthouse Audits:
- Chrome DevTools
- Command line interface
- Node.js module
- CI/CD integration
- Lighthouse web UI
Addressing Common Issues:
- Optimize images and assets
- Implement proper caching strategies
- Fix accessibility issues
- Ensure proper meta tags for SEO
- Add required manifest properties
- Configure proper service worker
Performance Best Practices
Techniques for fast-loading PWAs:
Critical Rendering Path Optimization:
- Minimize critical resources
- Reduce render-blocking resources
- Inline critical CSS
- Defer non-critical JavaScript
- Optimize font loading
Image Optimization:
- Responsive images with srcset
- WebP format where supported
- Lazy loading for off-screen images
- Proper image dimensions
- Image compression
Example Responsive Images:
<picture>
<source srcset="/images/hero-large.webp" media="(min-width: 800px)" type="image/webp">
<source srcset="/images/hero-large.jpg" media="(min-width: 800px)" type="image/jpeg">
<source srcset="/images/hero-small.webp" type="image/webp">
<img src="/images/hero-small.jpg" alt="Hero image" loading="lazy" width="400" height="300">
</picture>
JavaScript Optimization:
- Code splitting and lazy loading
- Tree shaking to remove unused code
- Minification and compression
- Efficient DOM manipulation
- Web workers for CPU-intensive tasks
Network Optimization:
- HTTP/2 or HTTP/3 support
- Preload critical resources
- Prefetch likely resources
- Resource hints (dns-prefetch, preconnect)
- Compression (Brotli, Gzip)
Example Resource Hints:
<!-- DNS prefetch -->
<link rel="dns-prefetch" href="https://api.weather-service.com">
<!-- Preconnect -->
<link rel="preconnect" href="https://api.weather-service.com" crossorigin>
<!-- Preload critical resources -->
<link rel="preload" href="/fonts/roboto-v20-latin-regular.woff2" as="font" type="font/woff2" crossorigin>
<!-- Prefetch likely to be needed resources -->
<link rel="prefetch" href="/js/weather-details.js">