Web Animation Patterns

Library Selection

CSS Animations

Use transform and opacity only (compositor-only, 60fps). Add will-change before animation, remove after. Use cubic-bezier() for spring-like easing.

Framer Motion

Use variants for orchestrated animations with staggerChildren. AnimatePresence wraps conditional renders for exit animations. layout prop animates layout changes. LazyMotion + domAnimation for code splitting (~30KB savings).

View Transitions API

Call document.startViewTransition(() => updateDOM()) with feature detection fallback. Use view-transition-name CSS for element persistence across transitions.

FLIP Technique

First, Last, Invert, Play -- animate layout changes at 60fps.

function flipAnimate(el: HTMLElement, update: () => void) {
  const first = el.getBoundingClientRect()    // First
  update()                                     // DOM change
  const last = el.getBoundingClientRect()      // Last
  const dx = first.left - last.left            // Invert
  const dy = first.top - last.top
  el.animate([
    { transform: `translate(${dx}px, ${dy}px)` },
    { transform: 'translate(0, 0)' },
  ], { duration: 300, easing: 'ease-out' })    // Play
}

Reduced Motion

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}

// Framer Motion respects this automatically, or override:
const prefersReduced = window.matchMedia('(prefers-reduced-motion: reduce)').matches

Gotchas

• Layout thrashing: batch reads before writes; never interleave getBoundingClientRect() with DOM mutations
• Compositor-only: only transform and opacity avoid layout/paint -- animating width, height, top, left is expensive
• will-change: add before animation, remove after; permanent will-change wastes GPU memory
• Framer Motion bundle: ~30KB min+gz; use LazyMotion + domAnimation feature for code splitting
• AnimatePresence: requires direct children with stable key props; fragments break exit animations
• View Transitions: still limited cross-browser; always feature-detect with document.startViewTransition

Cross-References

• frontend:responsive-web-design -- media queries and layout context for animation breakpoints
• frontend:accessibility-testing -- testing reduced-motion compliance and focus management