frame-rateFrame rate (FPS)
Inspect frame rate, long main-thread tasks, and dropped frames to diagnose jank.
Preview
Frame rate counts rendered frames per second; matching the display refresh cadence produces the smoothest result.
Preview
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Terms and distinctions
frame-rateFrame rate (FPS)
帧率（FPS）English definition
Frame rate counts rendered frames per second; matching the display refresh cadence produces the smoothest result.
Chinese translation
每秒渲染的帧数；动画与显示器刷新节奏匹配时通常最流畅。
jankJank
卡顿English definition
Jank is a perceptible break in motion caused by irregular frame timing or delayed main-thread work.
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English definition
A dropped frame occurs when rendering misses a display deadline and the previous image remains visible for another refresh.
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.
Before implementation
- Purpose
- Diagnose motion jank through frame rate, long tasks, and dropped frames with a reproducible performance baseline.
- Frequency
- Run on representative devices, after key motion changes, and before release, with ongoing monitoring for high-risk pages.
- Trigger
- Trigger from performance recordings, automated benchmarks, or real-user monitoring across cold and steady states.
- Enter / exit
- Update metrics immediately without decorative entrance motion that contaminates measurements.
- Interruptibility
- Allow recording to stop while preserving samples, and repeat tests with the same script and device conditions.
- Gesture and keyboard
- Use consistent gesture paths for scroll, drag, and click tests, cross-checking automated and manual runs.
- Reduced-motion strategy
- Measure default and reduced-motion modes separately, confirming the low-motion path also avoids long tasks.
Accessibility
Reduced motion
Measure default and reduced-motion modes separately, confirming the low-motion path also avoids long tasks.
Pre-delivery review
- Distinguish frame rate, an individual dropped frame, and visible jank.
- Record targets on both 60Hz and high-refresh displays.