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Bug: Web Vital Reporting Callback Timing Issue
The listenForWebVitalReportEvents function introduces two bugs:
- The
onHiddencallback now unconditionally calls_runCollectorCallbackOnce, which sets thecollectedflag totrue. This can occur before thepageloadSpanIdis available, preventing thecollectorCallbackfrom being triggered by subsequentnavigationevents. - A ReferenceError occurs because the
unsubscribeAfterStartPageLoadSpanvariable is accessed in thebeforeStartNavigationSpancallback before its declaration.
packages/browser-utils/src/metrics/utils.ts#L220-L237
sentry-javascript/packages/browser-utils/src/metrics/utils.ts
Lines 220 to 237 in f54d641
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AbhiPrasad
approved these changes
Jul 11, 2025
This was referenced Sep 29, 2025
This was referenced Oct 7, 2025
This was referenced Oct 15, 2025
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Our standalone web vital spans need to include the span id of the
pageloadspan s.t. we can correctly assign the web vital value to the respective pageload span in the Sentry backend.In the previous implementation, we'd simply wait for a tick after tracking the web vitals, get the active root span and take its spanId if it was a pageload span. However, this relies on the assumption that the pageload span is indeed started immediately. By default this happens but users can always deactivate default behaviour and call
startBrowserTracingPageloadSpanwhenever they want (for example, in a custombrowserTracingIntegration).Furthermore, this "wait for a tick" logic always bugged me and was only done because
getClient()would not yet return the already initialized client.This PR now makes the pageload spanId retrieval more robust by
afterStartPageloadSpan. This callback fires as soon as the pageload span is actually started and available.clientfrom thebrowserTracingIntegration'ssetuphook into the web vital listening function so that we can remove thesetTimeout(_, 0)logic.