Web Performance

Overview

Browser performance debugging via PerformanceObserver, with LoAF (long-animation-frame) as the primary signal. LoAF is the only entry type that, in one record, attributes a slow frame to a specific sourceURL + sourceFunctionName + sourceCharPosition + invokerType, with per-script forcedStyleAndLayoutDuration (sync reflow), pauseDuration (sync XHR / alert), and blockingDuration. Code inspection and performance.now() cannot reach this. Start with LoAFs, conclude from LoAFs.

When to use

Symptoms:

• Jank, dropped frames, janky scroll/swipe, complaints about frame rate
• Slow click / keypress / touch response, "unresponsive" complaints, poor INP
• Slow LCP, layout shifts (CLS)
• Animation stutter, transition jank, expensive renders during interaction

Do NOT use for: