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fix(scrollbar): place thumb correctly when it reappears #3003

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Merged
bajrangCoder merged 2 commits into from
Oct 29, 2026
Merged

fix(scrollbar): place thumb correctly when it reappears #3003

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ff23abd
fix(scrollbar): place thumb correctly when it reappears
bajrangCoder Oct 29, 2026
94dd1d2
fix(scrollbar): measure the track on every update while attached
bajrangCoder Oct 29, 2026
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18 changes: 16 additions & 2 deletions src/components/scrollbar/index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -192,11 +192,22 @@ export default function ScrollBar(options) {

if (height < 0) height = 0;
if (width < 0) width = 0;
if (render && height && width) setValue(scroll);
if (render && trackLength()) setValue(scroll);
}

/**
* Length the thumb travels along the scrollbar's axis. The cross axis is
* always 0 (the bar is thinner than the thumb), so only this one counts.
*/
function trackLength() {
return isVertical ? height : width;
}

function setValue(val) {
if (!height || !width) resize(false);
// Measure each time, as the parent can change size without a window
// resize (e.g. the sidebar opening). A detached bar has an empty rect;
// show() measures it once it's back on the page.
if ($scrollbar.isConnected) resize(false);

//Make sure value is between 0 and 1
if (val < 0) val = 0;
Expand Down Expand Up @@ -230,6 +241,9 @@ export default function ScrollBar(options) {
$scrollbar.classList.remove("hide");
if (!$scrollbar.isConnected) {
options.parent.append($scrollbar);
// The value may have been set while detached, against an empty
// rect; measure again so the thumb isn't painted at 0.
resize();
if (typeof onshow === "function") onshow();
}
}
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