performance

Performance

Core Web Vitals Targets

Metric	Target	Description
LCP (Largest Contentful Paint)	< 2.5s	Time until the largest visible content is rendered
INP (Interaction to Next Paint)	< 200ms	Latency from user interaction to visual response
CLS (Cumulative Layout Shift)	< 0.1	Visual stability — elements should not shift unexpectedly

Loading

• Code-split routes and heavy components with React.lazy + Suspense.
• Serve images in modern formats (WebP, AVIF) and always specify width and height to prevent layout shift.
• Minimize render-blocking resources: defer non-critical scripts, inline critical CSS.
• Preload critical assets (hero images, key fonts) with <link rel="preload">.

Rendering

• Wrap expensive pure components in React.memo only when props are stable (primitives or memoized references).
• Use useMemo to memoize expensive computed values and useCallback to stabilize callback references passed to memoized children.
• Virtualize long lists with a library like react-window or react-virtual — never render thousands of DOM nodes.
• Debounce high-frequency events (scroll, resize, input) to limit re-render rate.

Bundle Size

• Use named imports to enable tree-shaking: import { debounce } from 'lodash-es', not import _ from 'lodash'.
• Analyze bundle composition regularly with tools like webpack-bundle-analyzer or vite-bundle-visualizer.
• Load heavy third-party libraries (charts, editors, PDF renderers) with dynamic import() so they are not in the initial bundle.
• Avoid importing entire utility libraries when native browser APIs or a small helper will do.

Perceived Performance

• Use skeleton screens instead of spinners for content that has a known layout — reduces perceived wait time.
• Apply optimistic UI updates for low-risk mutations (likes, toggles) to make interactions feel instant.
• Prefetch the resources for likely next navigations using <link rel="prefetch"> or router-level prefetching.
• Load content progressively: show a low-quality placeholder first, then swap in the full asset once loaded.