[lexical] perf: defer DOM Selection property reads in $updateDOMSelection#8422
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Accessing `domSelection.anchorNode`, `.focusNode`, `.anchorOffset`, and
`.focusOffset` forces the browser to resolve the selection against the
current layout, triggering synchronous style/layout recalculation.
Previously these four properties were read eagerly at the top of
$updateDOMSelection, even when the function would immediately return
via one of two early-exit paths (collaboration tag check, or
`!isRangeSelection(nextSelection)`).
During initial mount, both `prevSelection` and `nextSelection` are null,
so the function hits the `!isRangeSelection` branch and returns — but
only after the browser has already paid the layout recalc cost for
property reads that are never consumed.
This commit:
- Keeps `document.activeElement` at the top (needed for the first
early return)
- Inlines `domSelection.anchorNode`/`.focusNode` in the
`isSelectionWithinEditor` call (only reached when
`prevSelection !== null`)
- Defers the four property reads to just before the diff-check block
that actually uses them
<!-- TODO: Replace with performance trace screenshot showing the
style/layout recalc cost before this fix -->
The net effect is zero layout-triggering Selection reads on mount and
on any code path that exits early.
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etrepum
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etrepum
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Apr 30, 2026
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It will be interesting to look at the performance trace after these changes |
Merged
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Summary
Accessing
domSelection.anchorNode,.focusNode,.anchorOffset, and.focusOffsetforces the browser to resolve the selection against the current layout, triggering synchronous style/layout recalculation.Previously these four properties were read eagerly at the top of
$updateDOMSelection, even when the function would immediately return via one of two early-exit paths:!isRangeSelection(nextSelection)(the common case on mount)During initial mount, both
prevSelectionandnextSelectionare null, so the function hits the!isRangeSelectionbranch and returns — but only after the browser has already paid the layout recalc cost for property reads that are never consumed.Performance trace
Changes
document.activeElementat the top (needed for the first early return)domSelection.anchorNode/.focusNodedirectly in theisSelectionWithinEditorcall (only reached whenprevSelection !== null)anchorNode,focusNode,anchorOffset,focusOffset) to just after the early returns, right before the diff-check block that actually uses themImpact
Zero layout-triggering
Selectionreads on mount and on any code path that exits early. This eliminates unnecessary forced style/layout recalculations during Lexical node mounting.