Buffered flag for long tasks

This feature tracks https://www.chromestatus.com/feature/5118272741572608 for the case of PerformanceLongTask entries

We initially shipped the PerformanceObserverInit buffered flag without longtasks because PerformanceLongTaskTiming entries are not currently being created if there is no PerformanceObserver observing them. There is no need for these entries without the buffered flag because there is no PerformanceTimeline support for longtasks: they cannot be queried via performance.getEntries(). Nonetheless, Blink’s PerformanceMonitor already receives task durations, so creating these entries would be pretty trivial. Buffering these entries is useful because many longtasks occur early during page load. Without the buffered flag, a developer cannot gain insight into very early long tasks and is incentivized to run a script registering a PerformanceObserver early on.



Established standard

Status in Chromium


Enabled by default (tracking bug) in:

  • Chrome for desktop release 81
  • Chrome for Android release 81
  • Android WebView release 81

Consensus & Standardization

After a feature ships in Chrome, the values listed here are not guaranteed to be up to date.

  • Positive
  • No signal
  • No signal
  • Strongly positive


Last updated on 2020-08-01