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Skip phantom scroll events #135

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Merged
cyanzhong merged 1 commit into from
Jun 10, 2026
+308 −297
Merged

Skip phantom scroll events #135

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76 changes: 38 additions & 38 deletions dist/lite/markedit-preview.js
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510 changes: 255 additions & 255 deletions dist/markedit-preview.js
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19 changes: 15 additions & 4 deletions src/scroll.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -7,17 +7,26 @@ export function startObserving(sourcePane: HTMLElement, targetPane: HTMLElement)
return;
}

// Skip phantom scroll events where the editor didn't actually move
states.lastSourceScrollTop = sourcePane.scrollTop;
const didScroll = () => {
if (Math.abs(sourcePane.scrollTop - states.lastSourceScrollTop) < 0.5) {
return;
}

states.lastSourceScrollTop = sourcePane.scrollTop;
syncScrollProgress(sourcePane, targetPane);
};

if ('onscrollend' in window) {
sourcePane.addEventListener('scrollend', () => syncScrollProgress(sourcePane, targetPane));
sourcePane.addEventListener('scrollend', didScroll);
} else {
sourcePane.addEventListener('scroll', () => {
if (states.scrollUpdater !== undefined) {
clearTimeout(states.scrollUpdater);
}

states.scrollUpdater = setTimeout(() => {
syncScrollProgress(sourcePane, targetPane);
}, 100);
states.scrollUpdater = setTimeout(didScroll, 100);
});
}
}
Expand Down Expand Up @@ -135,7 +144,9 @@ function clampProgressValue(value: number) {
}

const states: {
lastSourceScrollTop: number;
scrollUpdater: ReturnType<typeof setTimeout> | undefined;
} = {
lastSourceScrollTop: 0,
scrollUpdater: undefined,
};