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fix: thread panel not scrolling to bottom after sending a reply #40956

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Merged
dionisio-bot merged 2 commits into from
Jun 16, 2026
Merged

fix: thread panel not scrolling to bottom after sending a reply #40956

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2a6a574
fix: thread panel not scrolling to bottom after sending a reply
MartinSchoeler Jun 15, 2026
a66ce69
Create old-cities-enjoy.md
MartinSchoeler Jun 15, 2026
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5 changes: 5 additions & 0 deletions .changeset/old-cities-enjoy.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
"@rocket.chat/meteor": patch
---

fixes issue that caused threads to sometimes not scroll when sending messages
20 changes: 19 additions & 1 deletion apps/meteor/client/views/room/contextualBar/Threads/components/ThreadMessageList.tsx
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Expand Up @@ -75,6 +75,7 @@ const ThreadMessageList = ({ mainMessage, shouldJumpToBottom, setShouldJumpToBot

const virtualizerRef = useRef<VirtualizerHandle | null>(null);
const isAtBottom = useRef<boolean | null>(null);
const prevItemsLengthRef = useRef(0);

const { keepAtBottomRef, setKeepAtBottom } = useKeepAtBottom(isAtBottom);
const messagesLength = messages.length;
Expand Down Expand Up @@ -109,6 +110,7 @@ const ThreadMessageList = ({ mainMessage, shouldJumpToBottom, setShouldJumpToBot

useEffect(() => {
lastThreadJumpKeyRef.current = undefined;
prevItemsLengthRef.current = 0;
}, [mainMessage._id]);

useEffect(() => {
Expand All @@ -120,15 +122,31 @@ const ThreadMessageList = ({ mainMessage, shouldJumpToBottom, setShouldJumpToBot
setShouldJumpToBottom(false);
return;
}

// Scroll to bottom when current user's optimistic (temp) message is appended.
// Fires before server confirmation, giving immediate scroll feedback.
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const prev = prevItemsLengthRef.current;
prevItemsLengthRef.current = items.length;
if (items.length > prev && uid) {
const lastItem = items.at(-1);
if (lastItem?.temp && lastItem.u._id === uid) {
setShouldJumpToBottom(true);
}
}

if (isAtBottom.current === true && lastScrollSizeRef.current !== handle?.scrollSize) {
lastScrollSizeRef.current = handle?.scrollSize ?? 0;
setShouldJumpToBottom(true);
}
if (shouldJumpToBottom) {
// Optimistically mark as at-bottom before the scroll executes (rAF).
// This ensures the ResizeObserver in useKeepAtBottom re-scrolls if
// quote/attachment content grows between now and when Virtua fires the scroll.
isAtBottom.current = true;
handle.scrollToIndex(items.length, { align: 'end' });
setShouldJumpToBottom(false);
}
}, [loading, items.length, msgJumpParam, threadMsgTargetIndex, shouldJumpToBottom, setShouldJumpToBottom]);
}, [items, loading, msgJumpParam, threadMsgTargetIndex, shouldJumpToBottom, setShouldJumpToBottom, uid]);

useEffect(() => {
if (threadMsgTargetIndex < 0 || !msgJumpParam) {
Expand Down
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