Frontend Errors : Animation Jank

Diagnostic skill. The reader has a symptom (dropped frames, slow tap, scroll stutter, ResizeObserver warning) and needs to find the root cause and fix it. The companion skill [[frontend-perf-animation-gpu-containment]] teaches the prescriptive rules; this skill teaches how to find violations.

Quick Reference

Frame budget at 60 Hz / 120 Hz / 144 Hz

Per MDN : requestAnimationFrame (verified 2026-05-19), browsers call rAF callbacks at the display refresh rate :

For all main-thread work in a single frame (event handlers + style + layout + paint + composite + your JS), you have ONE frame budget. Going over even once means a dropped frame.