core: update cumulative-layout-shift #12554
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adamraine
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May 25, 2021
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| // The original Cumulative Layout Shift metric, the sum of main-frame shift events from the entire trace. | ||
| const oldCumulativeLayoutShift = mainFrameShiftEvents | ||
| .reduce((sum, e) => sum += e.weightedScore, 0); |
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calculateOldCumulativeLayoutShift?
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ah yeah, thanks
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ok, we're going with |
connorjclark
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May 25, 2021
adamraine
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May 25, 2021
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Fixes #12350, part of #11866
As discussed in that issue, CLS is being switched to the
max-session-gap1s-limit5svariant with LayoutShift events from the whole frame tree ("all frames") to align with the broader web-vitals CLS change.The new version will result in unchanging or better CLS values for all users by design, but since Lighthouse currently only measures CLS during page load, most users won't see much meaningful change in their CLS (we currently estimate that about 5% of sites will go from a poor to average rating, and about 3% of sites will move from average to passing).
This PR touches a lot of files, but the primary change is moving the winning variant in
layout-shift-variantsto thecumulative-layout-shiftcomputed artifact (with much oflayout-shift-variants-testmaking a similar journey) and then updating a ton of test expectations.The computed artifact also exposes a
cumulativeLayoutShiftMainFramefor a only-main-frame version of the metric, and anoldCumulativeLayoutShifttotalCumulativeLayoutShift) which is the original CLS for developers who still want to track it.I can't remember what we finally decided to call that and #12350 isn't clear, so that'll be the first thing we can fix in review :)