feat(browser): Add ElementTiming instrumentation and spans #16589
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size-limit report 📦
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AbhiPrasad
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Jun 16, 2025
| // - `renderTime` if available (available for all entries, except 3rd party images, but these should be covered by `loadTime`, 0 otherwise) | ||
| // - `timestampInSeconds()` as a safeguard | ||
| // see https://developer.mozilla.org/en-US/docs/Web/API/PerformanceElementTiming/renderTime#cross-origin_image_render_time | ||
| const { spanStartTime, spanStartTimeSource } = loadTime |
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this can be a helper or return tuples, will help reduce bundle size of spanStartTime and spanStartTimeSource being un-minifiable.
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| const activeSpan = getActiveSpan(); | ||
| const rootSpan = activeSpan ? getRootSpan(activeSpan) : undefined; | ||
| const route = rootSpan ? spanToJSON(rootSpan).description : getCurrentScope().getScopeData().transactionName; |
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we can move these outside of the loop to avoid having to keep calling spanToJSON
s1gr1d
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Jun 30, 2025
This PR implements sending standalone LCP spans as an opt-in feature. Behaviour-wise, it's mostly aligned with our prior implementation of sending CLS standalone spans (#13056): - add an `_experiments.enableStandaloneLcpSpans` option and treat it as opt-in - keep collecting LCP values until users soft-navigate or the page is hidden - then, send the LCP span once - adds all `lcp.*` span attributes as well as the `lcp` measurement to the span (depending on if we merge #16589 or this first, we might need to readjust size limit) closes #13063 --------- Co-authored-by: s1gr1d <[email protected]> Co-authored-by: Sigrid Huemer <[email protected]>
# Conflicts: # .size-limit.js
![cursor[bot]](https://avatars.githubusercontent.com/in/1210556?s=60&v=4){kind=small}
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Bug: ElementTiming Timing Inconsistencies
ElementTiming spans for image-paint entries have inconsistent timing due to how loadTime and renderTime are used for span start time and duration calculation, especially when one of these values is 0 (e.g., for cross-origin images without CORS). This leads to:
- Zero-duration spans starting at
loadTimewhenrenderTimeis 0 butloadTimeis present. - Spans ending at
2 * renderTimewhenloadTimeis 0 butrenderTimeis present, as duration is incorrectly calculated asrenderTime.
packages/browser-utils/src/metrics/elementTiming.ts#L71-L85
sentry-javascript/packages/browser-utils/src/metrics/elementTiming.ts
Lines 71 to 85 in f6b225c
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s1gr1d
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This was referenced Sep 29, 2025
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This PR adds support for instrumenting and sending spans from
ElementTimingAPI entries. Just like with web vitals and long tasks/animation frames, we register aPerformanceObserverand extract spans from newly emitted ET entries.Important:
enableElementTiming: falseinbrowserTracingIntegrationnavigationspans as well). We could also go the route of only sending until the first navigation as with standalone CLS/LCP spans. Happy to accept any direction we wanna take this.Some noteworthy findings while working on this:
loadTimewhich is the relative timestamp to the browser'stimeOrigin, when the image finished loading. For text nodes,loadTimeis always0, since nothing needs to be loaded.renderTimewhich is the relative timestamp to the browser'stimeOrigin, when the node finished rendering (i.e. was painted by the browser).renderTime - loadTimefor image nodes0for text nodestimeOrigin + loadTimefor image nodestimeOrigin + renderTimefor text nodesIn addition to the raw span and conventional attributes, we also collect a bunch of ET-specific attributes:
element.type- tag name of the element (e.g.imgorp)element.size- width x height of the elementelement.render-time-entry.renderTimeelement.load-time-entry.loadTimeelement.url- url of the loaded image (undefinedfor text nodes)element.identifier- the identifier passed to theelementtiming=identifierHTML attributeelement.paint-type- the node paint type (image-paintortext-paint)also some additional sentry-sepcific attributes:
route- the route name, either from the active root span (if available) or from the scope'stransactionNamesentry.span-start-time-source- the data point we used as the span start timeMore than happy to adjust any of this logic or attribute names, based on review feedback :)
closes #13675
also ref #7292