Frontend Performance
Frontend performance shapes how users perceive your entire application. A fast backend means nothing if the browser takes seconds to render content. Google's Core Web Vitals have become the industry standard for measuring what users actually experience, and optimizing for them improves both user satisfaction and search rankings.
Core Web Vitals Explained
Largest Contentful Paint (LCP) measures when the main content becomes visible. This is typically your hero image, main heading, or primary content block. Target under 2.5 seconds — users shouldn't wait longer to see what they came for.
First Input Delay (FID) measures interactivity. When a user clicks a button, how long until the browser responds? Heavy JavaScript execution blocks the main thread, making pages feel unresponsive. Target under 100 milliseconds.
Cumulative Layout Shift (CLS) measures visual stability. Have you ever tried to click a button, only to have the page shift and you click something else? That's layout shift. Target a score under 0.1 by reserving space for images and dynamic content.
Image Optimization
Images typically account for most page weight. Optimize them aggressively:
Use modern formats like WebP or AVIF, which provide better compression than JPEG or PNG. Serve appropriately sized images — don't send a 4000px image to display at 400px. Implement lazy loading so images below the fold don't block initial render.
<img src="photo.webp" loading="lazy" width="400" height="300" alt="Description">
Always include width and height attributes to prevent layout shift as images load.
Code Optimization
Code splitting loads only what's needed for the current page. Modern bundlers like Webpack and Vite support this automatically with dynamic imports. Users shouldn't download your entire application to view the homepage.
Minification removes whitespace and shortens variable names, reducing file sizes by 30-50%. Every build tool supports this — ensure it's enabled for production.
Compression with gzip or Brotli further reduces transfer sizes. Configure your server or CDN to compress text-based assets automatically.
Caching and CDNs
Proper cache headers let browsers store assets locally, eliminating network requests on repeat visits. Static assets with content-based filenames can be cached indefinitely.
Content Delivery Networks serve assets from locations near your users, reducing latency dramatically for global audiences.
Measuring Performance
Lighthouse in Chrome DevTools provides instant audits with specific recommendations. Run it in incognito mode to avoid extension interference.
WebPageTest offers detailed waterfall charts showing exactly what loads when. It tests from real locations worldwide.
The Chrome User Experience Report provides real-world performance data from actual Chrome users, showing how your site performs in the wild.