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refactor: avoid forced style recalculation on scroll #10150

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Merged
merged 1 commit into from
Sep 11, 2025
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refactor: avoid forced style recalculation on scroll #10150

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8 changes: 3 additions & 5 deletions packages/component-base/src/virtualizer-iron-list-adapter.js
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Original file line number Diff line number Diff line change
Expand Up @@ -547,8 +547,8 @@ export class IronListAdapter {
return;
}

this._adjustVirtualIndexOffset(this._scrollTop - (this.__previousScrollTop || 0));
const delta = this.scrollTarget.scrollTop - this._scrollPosition;
this._adjustVirtualIndexOffset(this._scrollTop - this._scrollPosition);
const delta = this._scrollTop - this._scrollPosition;

super._scrollHandler();

Expand Down Expand Up @@ -601,11 +601,9 @@ export class IronListAdapter {
);
}

this.__previousScrollTop = this._scrollTop;
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@vursen vursen Sep 11, 2025 •
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_scrollTop reads the actual scrollTop value from the DOM, which can force a style recalculation if done immediately after style writes.


// If the first visible index is not 0 when scrolled to the top,
// scroll to index 0 to fix the issue.
if (this._scrollTop === 0 && this.firstVisibleIndex !== 0 && Math.abs(delta) > 0) {
if (this._scrollPosition === 0 && this.firstVisibleIndex !== 0 && Math.abs(delta) > 0) {
this.scrollToIndex(0);
}
}
Expand Down