Client-Side Performance, Rendering, and Web Vitals
Performance as user experience
Why performance matters
Performance influences trust, conversion, comprehension, and perceived quality. Advanced teams treat performance as a design constraint measured by metrics, not a vague aspiration.
Performance concepts
Latency
The delay before a response or update is experienced.
Throughput
The amount of work completed over time.
Main thread blocking
Work that prevents timely input handling or rendering.
Perceived performance
How fast the experience feels to a user.
Optimization levers
| Area | Typical techniques |
|---|---|
| Network | Compression, caching, fewer requests, prioritization |
| JavaScript | Code splitting, tree shaking, avoiding unnecessary work |
| Rendering | Reducing reflows, batching updates, virtualization |
| Assets | Responsive images, modern formats, font optimization |