feat(rrweb): attributeFilter option for native MutationObserver filtering (adopt upstream #1873) - #4129
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…iltering Port of upstream rrweb #1873. When session_recording.attributeFilter is set, the list is passed through to MutationObserver.observe so mutations to unlisted attributes never fire the observer callback at all - zero recording CPU for e.g. inline-style animation churn. Beyond the upstream diff: the filter is also wired into the shadow-DOM manager's bypassOptions so it applies inside shadow roots (upstream only covered the main document), and an empty array is treated as unset so a bad config value cannot silently disable attribute recording. Off by default; no behaviour change unless configured. Generated-By: PostHog Code Task-Id: b089f2a6-9e07-4abf-aae1-cda53f9d8f56
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posthog-js Compliance ReportDate: 2026-07-11 13:42:25 UTC ✅ All Tests Passed!26/26 tests passed Capture Tests✅ 26/26 tests passed View Details
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Size Change: +4.45 kB (+0.03%) Total Size: 17.4 MB
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pauldambra
marked this pull request as ready for review
July 11, 2026 15:33
pauldambra
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TueHaulund,
arnohillen,
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ksvat
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July 11, 2026 15:33
arnohillen
approved these changes
Jul 14, 2026
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Problem
Adopts upstream rrweb #1873 (open, reviewed line-by-line before porting), tracked in #3765 — the biggest recording-performance lever in the batch-1 adoption plan.
CSS/JS animations (carousels, sliders, animated badges) generate 1,000+ inline-
styleattribute mutations per second with zero user interaction; on some sites nearly all recorded events are attribute mutations from animations. Today there is no way to stop these before they cost CPU:ignoreCSSAttributesonly intercepts CSSOMsetPropertycalls, and ourMutationThrottlerdrops events after rrweb has already done the expensive serialization work.Changes
session_recording.attributeFilter: string[]— passed straight through to the nativeMutationObserver.observe({ attributeFilter }), so mutations to unlisted attributes never fire the observer callback at all (zero per-mutation CPU, in every frame the observer covers).bypassOptions, so it applies inside shadow roots (upstream only covered the main document — web-component-heavy sites are exactly where animation floods live); same-origin iframes get it via the sharedobserve(doc)pathstyle).Refs #3765.
Release info Sub-libraries affected
Libraries affected
Checklist
packages/rrweb/rrweb/test/record/attribute-filter.test.tscovering main doc, shadow roots, empty-array safety, and that childList/characterData are unaffected; jest test for the config passthrough)If releasing new changes
pnpm changesetto generate a changeset file🤖 Agent context
Autonomy: Human-driven (agent-assisted)
Ported as part of the batch-1 (recording-performance-first) adoption plan on #3765 (PostHog Code session). The upstream PR is from a low-trust author, so the diff was reviewed line-by-line rather than cherry-picked; review found the shadow-DOM gap and the empty-array footgun fixed above. Verified via the existing rrweb record suite (34/34), the new 5-test puppeteer suite, the full lazy-sessionrecording jest suite (240/240), and the types config-snapshot test.
Created with PostHog Code