fix(web): remove animated attributes when value is undefined#2439
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`applyAnimatedValues` previously called `setAttribute(name, undefined)`, which coerces to the string "undefined". For boolean-style attributes like `inert` or `disabled`, the attribute's presence is what matters — "undefined" keeps them active. The attribute must be removed entirely. Now: when an animated value resolves to `undefined`, the attribute is removed via `removeAttribute`. The same applies to `viewBox`, `className`, and `children` (which clears `textContent`). Defined falsy values such as `0` or `""` continue to flow through `setAttribute`. Co-authored-by: LoganDark <github@logandark.mozmail.com>
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🦋 Changeset detectedLatest commit: e65c1bd The changes in this PR will be included in the next version bump. This PR includes changesets to release 12 packages
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This was referenced May 21, 2026
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Summary
Animated DOM attributes whose value resolves to
undefinedare now removed viaremoveAttributeinstead of coerced to the string"undefined". Boolean-style attributes likeinertanddisabledwere broken because their presence enables them — any value (including"undefined") keeps them active. The same fix applies toviewBox,className, andchildren(which now clearstextContent).Defined falsy values such as
0or""are unaffected and still go throughsetAttribute.Tests
Six new cases in
targets/web/src/animated.test.tsxunderanimated component attribute removal:inertremoved when its animated value becomesundefineddata-foo) removed when value becomesundefinedviewBoxremoved when value becomesundefinedclassNameremoved when value becomesundefinedchildrenclearstextContentwhen value becomesundefinedtabIndex={'0'}) still applied viasetAttributeTests use a small
TestFluid<T>helper that extendsFluidValueso a value can transition toundefined(whichSpringValueitself does not support).Notes
Closes #2319 by @LoganDark, rebased onto
nextand extended to handleclassName(per reviewer comment on the original PR). Original author credited viaCo-authored-byon the commit.