Frame rate (FPS)
Inspect frame rate, long main-thread tasks, and dropped frames to diagnose jank.
Preview
Live preview
Frames drawn per second. 60fps is the baseline for smooth motion; 120fps on newer displays.
Authoritative vocabulary
Definition and close-term distinctions
English definitions are preserved verbatim from Animation Vocabulary; translations and distinctions help you choose precisely.
frame-rateFrame rate (FPS)
帧率（FPS）Authoritative definition
Frames drawn per second. 60fps is the baseline for smooth motion; 120fps on newer displays.
Chinese translation
每秒绘制的帧数；60fps 是流畅运动的基线，新款显示器可达到 120fps。
jankJank
卡顿Authoritative definition
Visible stutter when the browser drops frames because it can't keep up with the animation.
Chinese translation
浏览器无法跟上动画并发生掉帧时出现的可见停顿。
Distinction
Jank is the visible stutter a user sees; Frame rate is the metric used to measure drawing speed.
dropped-frameDropped frame
丢帧Authoritative definition
A frame the browser missed its deadline to draw, causing a tiny hitch in motion.
Chinese translation
浏览器未能在截止时间前绘制的一帧，会让运动出现轻微顿挫。
Distinction
Dropped frame is one missed drawing deadline; Frame rate summarizes drawing frequency over time.
Design contract
Decide before this motion ships
Purpose, frequency, trigger, timing, interruptibility, and gesture rules shape the implementation.
Diagnose motion jank through frame rate, long tasks, and dropped frames with a reproducible performance baseline.
Run on representative devices, after key motion changes, and before release, with ongoing monitoring for high-risk pages.
Trigger from performance recordings, automated benchmarks, or real-user monitoring across cold and steady states.
Update metrics immediately without decorative entrance motion that contaminates measurements.
Allow recording to stop while preserving samples, and repeat tests with the same script and device conditions.
Use consistent gesture paths for scroll, drag, and click tests, cross-checking automated and manual runs.
Measure default and reduced-motion modes separately, confirming the low-motion path also avoids long tasks.
Review notes
Pre-delivery review
- Distinguish frame rate, an individual dropped frame, and visible jank.
- Record targets on both 60Hz and high-refresh displays.
Accessibility
Keep information accessible
Reduced motion
Measure default and reduced-motion modes separately, confirming the low-motion path also avoids long tasks.