JS Self-Profiling API

Category: Performance
Type: New or changed feature
Status: Enabled by default (Chrome 94)
Intent stage: Shipped

Summary

Adds a web-exposed sampling profiler for measuring client JavaScript execution time. Gathering JS profiles from real users can help developers debug slow observed performance without the need for invasive manual instrumentation.

Motivation

Currently, it is difficult for web developers to understand how their applications perform in the wide variety of conditions encountered on real user devices. A native self-profiling API for JS code would also allow web developers to efficiently find hotspots in their JS code during page loads and user interactions, to assign CPU budgets to individual JS-implemented features on the page, to find unnecessary work being done on the client, and to find low-priority JS code executing in the background and wasting device power.

Standards & signals

Specification: https://wicg.github.io/js-self-profiling/
Firefox: No signal
Safari: Negative
Web developers: Strongly positive — Facebook has been driving development of this API, and has been able to debug and resolve a wide variety of performance issues during the origin trial period. We have also seen quite a bit of support from other developers: Microsoft: https://github.com/WICG/js-self-profiling/issues/24 Elastic: https://github.com/WICG/js-self-profiling/issues/21 Boomerang: https://github.com/WICG/js-self-profiling/issues/14 Dropbox: https://github.com/WICG/js-self-profiling/issues/9
Tracking bug: https://bugs.chromium.org/p/chromium/issues/detail?id=956688

Docs: https://docs.google.com/document/d/1NGrU6xVWHq8uLfSFRfDWh1v_UiXLiOgr2FDb2KIaoL0/edit?usp=sharing https://docs.google.com/document/d/1OTwlBnAMXZEaOICtuz16c01QnkPPdqHBoHpfGwnk5SY/edit?usp=sharing

Samples: https://wicg.github.io/js-self-profiling/#examples

Explainers: https://www.github.com/WICG/js-self-profiling

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