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fix(runtime-dom): inconsistent behaviour on nested transition groups #8803

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fix(runtime-dom): inconsistent behaviour on nested transition groups #8803

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60f3886
fix(runtime-dom): inconsistent behaviour on nested transition groups …
Jul 18, 2023
4da6b29
refactor(runtime-dom): use simple Position object instead of DOMRect …
Jun 13, 2024
3abe763
Merge branch 'main' into fix/nested-transitiongroup
Jun 24, 2024
f3ea4b8
Merge branch 'main' into fix/nested-transitiongroup
daniser Jul 8, 2024
dcc93a8
Merge branch 'main' into fix/nested-transitiongroup
edison1105 Aug 20, 2024
ff6a6b0
Merge branch 'vuejs:main' into fix/nested-transitiongroup
daniser Sep 16, 2024
29a1647
Merge branch 'main' into fix/nested-transitiongroup
edison1105 Nov 4, 2024
83895e7
Merge branch 'vuejs:main' into fix/nested-transitiongroup
daniser Nov 22, 2024
b48c5a4
Merge branch 'main' into fix/nested-transitiongroup
edison1105 Jun 11, 2025
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32 changes: 25 additions & 7 deletions packages/runtime-dom/src/components/TransitionGroup.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -29,8 +29,13 @@ import {
} from '@vue/runtime-core'
import { extend } from '@vue/shared'

const positionMap = new WeakMap<VNode, DOMRect>()
const newPositionMap = new WeakMap<VNode, DOMRect>()
interface Position {
left: number
top: number
}

const positionMap = new WeakMap<VNode, Position>()
const newPositionMap = new WeakMap<VNode, Position>()
const moveCbKey = Symbol('_moveCb')
const enterCbKey = Symbol('_enterCb')

Expand Down Expand Up @@ -145,10 +150,7 @@ const TransitionGroupImpl: ComponentOptions = /*@__PURE__*/ decorate({
instance,
),
)
positionMap.set(
child,
(child.el as Element).getBoundingClientRect(),
)
positionMap.set(child, getRelativePosition(child.el as Element))
}
}
}
Expand Down Expand Up @@ -188,8 +190,24 @@ function callPendingCbs(c: VNode) {
}
}

function getRelativePosition(el: Element): Position {
const elRect = el.getBoundingClientRect()
if (!el.parentElement) {
return {
left: elRect.left,
top: elRect.top,
}
}

const parentRect = el.parentElement.getBoundingClientRect()
return {
left: elRect.left - parentRect.left,
top: elRect.top - parentRect.top,
}
}
Comment on lines +193 to +207
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⚠️ Potential issue

parentElement may be null – relative delta becomes wrong

getRelativePosition falls back to absolute viewport coords when el.parentElement is null (e.g. the parent is a DocumentFragment, a comment, or the node is temporarily detached).
If that happens between the “old” and “new” snapshots, dx/dy will be computed against mixed coordinate spaces → items jump instead of animating.

Proposed defensive tweak:

function getRelativePosition(el: Element): Position {
-  const elRect = el.getBoundingClientRect()
-  if (!el.parentElement) {
-    return {
-      left: elRect.left,
-      top: elRect.top,
-    }
-  }
-
-  const parentRect = el.parentElement.getBoundingClientRect()
+  const elRect = el.getBoundingClientRect()
+  const parent = el.parentElement as Element | null
+  if (!parent) {
+    // No element parent (e.g. DocumentFragment) — treat the container itself
+    // as the reference so both snapshots stay in the same coordinate space.
+    return { left: elRect.left, top: elRect.top }
+  }
+
+  const parentRect = parent.getBoundingClientRect()
   return {
     left: elRect.left - parentRect.left,
     top: elRect.top - parentRect.top,
   }
 }

This keeps both snapshots in the same space and avoids incorrect deltas.

Committable suggestion skipped: line range outside the PR's diff.

🤖 Prompt for AI Agents 
In packages/runtime-dom/src/components/TransitionGroup.ts around lines 193 to
207, the getRelativePosition function returns absolute viewport coordinates when
el.parentElement is null, causing inconsistent coordinate spaces and incorrect
delta calculations. To fix this, modify the function to always compute positions
relative to a consistent ancestor or coordinate space, such as the document or a
stable container, ensuring both old and new snapshots use the same reference
frame and preventing animation jumps.


function recordPosition(c: VNode) {
newPositionMap.set(c, (c.el as Element).getBoundingClientRect())
newPositionMap.set(c, getRelativePosition(c.el as Element))
}

function applyTranslation(c: VNode): VNode | undefined {
Expand Down