Intent to extend origin trial: Pending Beacon API

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Ming-Ying Chung

May 9, 2023, 2:03:36 AM5/9/23
to blink-dev, Yoav Weiss, Daisuke Enomoto, Fergal Daly,, Ian Clelland,

API owners,

We would like to extend the origin trial for 3 additional milestones, with the extension starting in 113 continuing through 115. The OT was previously approved to run from 107 to 112 (OT token expires on 2023-06-02).

Contact emails,,,



Design docs


A stateful PendingBeacon API allows website authors to specify one or more beacons (HTTP requests) that should be sent reliably when the page is being unloaded.


Existing beacon APIs are all based around a developer constructing and sending a beacon, and there's no good time for that "send" call to be made. (Handlers such as 'unload' are often ignored, for example.) This API delegates the sending to the browser itself, so it can support beacons on page unload or on page hide, without the developer having to implement send calls at exactly the right times.

Blink component


TAG review

TAG review status





Interoperability and Compatibility



Gecko: pending further feedback:


WebKit: Positive signal (closed): / 


Web developers: No signals


Other signals: ongoing API discussion in










Goals for experimentation

  • Collect usability feedback about the current API shape to decide how to improve the API design

  • Collect stability metrics of the current API implementation

Reason this experiment is being extended

The new API shape is currently being discussed with WebKit Fetch folks. It is unlikely that we will ship the current OT version of the API.

At the same time, we have received additional feedback after the previous OT extension. There are users currently trying to evaluate the API with their usage and need more time to collect the metrics, but our OT token will expire in early June. We would like to request an extension to help both of us.


Ongoing technical constraints

See “What’s not supported


Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)?



Is this feature fully tested by web-platform-tests?



Flag name


or via Origin Trial Token


Tracking bug


Launch bug


Estimated milestones

OriginTrial desktop last (new request)


OriginTrial desktop last


OriginTrial desktop first


OriginTrial desktop last (new request)


OriginTrial Android last


OriginTrial Android first



Link to entry on the Chrome Platform Status


Links to previous Intent discussions

Intent to prototype:

Intent to Experiment:

Read for Trial:

Yoav Weiss

May 9, 2023, 3:00:20 AM5/9/23
to Ming-Ying Chung, blink-dev, Daisuke Enomoto, Fergal Daly,, Ian Clelland,
LGTM to extend experimentation M113-115

I appreciate your engagement with WebKit & Fetch folks and your willingness to modify the API shape based on feedback. I think that can easily count as progress towards shipping, which is required for extending the OT. The fact that the current shape is unlikely to ship as is is also reassuring (as it reduces the risk of burn-in following a long trial).
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