Web-Facing Change PSA: Update LongTask code to use Long animation frames as a backend
Noam Rosenthal
Contact emails
nrose...@chromium.org
Specification
https://w3c.github.io/longtasks
Summary
Using the LoAF implementation for reporting longtasks is an implementation detail, but it would have the following web-observable impact: - we would stop reporting longtasks for hidden tabs - a few longtask bugs would disappear, resulting in more reported longtasks Note that this would not affect the Lighthouse TBT score, that anyway relies on trace events.
Blink component
Blink>PerformanceAPIs
TAG review
None
TAG review status
Not applicable
Risks
Interoperability and Compatibility
This doesn't change the spec, and mostly improves maturity and maintainability. The main compat risk is with the behavior change that longtasks in hidden tabs are not reported, however that's anyway a brittle concept as background documents often undergo all kinds of throttling, making their reported longtasks not actionable.
Gecko: N/A
WebKit: N/A
Web developers: No signals
Other signals:
This doesn't change the spec, and mostly improves maturity and maintainability. The main compat risk is with the behavior change that longtasks in hidden tabs are not reported, however that's anyway a brittle concept as background documents often undergo all kinds of throttling, making their reported longtasks not actionable.
Gecko: N/A
WebKit: N/A
Web developers: No signals
Other signals:
WebView application risks
Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?
None
Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?
None
Debuggability
None
Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?
Yes
Is this feature fully tested by web-platform-tests?
Yes
Existing tests: https://wpt.fyi/results/longtask-timing?label=experimental&label=master&aligned This would fix some of them.
Flag name on chrome://flags
LongTaskFromLongAnimationFrame
Finch feature name
LongTaskFromLongAnimationFrame
Requires code in //chrome?
False
Tracking bug
https://issues.chromium.org/issues/40266553
Estimated milestones
| Shipping on desktop | 124 |
| Shipping on Android | 124 |
| Shipping on WebView | 124 |
Anticipated spec changes
Open questions about a feature may be a source of future web compat or interop issues. Please list open issues (e.g. links to known github issues in the project for the feature specification) whose resolution may introduce web compat/interop risk (e.g., changing to naming or structure of the API in a non-backward-compatible way).
None