fix(custom-element): prevent parse slot when custom elemnt move in DOM

[AliGhasami]

Bug Report: Component Disappears When Moved in DOM Using Custom Element with Slot

Description

I'm using a Custom Element to wrap a Vue component that includes a slot. In this setup, shadowRoot is set to false.

The issue I'm encountering is that when I move this element within the DOM — either by dragging it or using appendChild to insert it elsewhere — the disconnectedCallback is triggered.

Inside the disconnectedCallback, nextTick is used. However, before nextTick gets a chance to execute, the connectedCallback is triggered again. As a result, _parseSlots is called before the component is fully re-initialized, and all childNodes inside the element are removed. This causes the component to suddenly disappear from the DOM.

Temporary Fix

To resolve this issue, I added a check to ensure _instance is not null before calling _parseSlots. This workaround prevents the unexpected removal of slot content.

Reproduction

If needed, I can provide a minimal reproduction of the problem.

Environment

• Vue version: [your version]
• Custom Element setup: shadowRoot: false
• Browser: [your browser name and version]

Expected Behavior

Moving the component in the DOM should not cause it to lose its slotted children or disappear.

Actual Behavior

Slotted content is removed when the component is reconnected before nextTick executes.

---

Let me know if a repro is needed — I’d be happy to provide one.

[edison1105]

thanks for the PR.could you please add a test ?

[github-actions]

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	100 kB (+16 B)	38.1 kB (+4 B)	34.4 kB (+20 B)
vue.global.prod.js	158 kB (+16 B)	58.3 kB (+1 B)	51.9 kB (-6 B)

Usages

Name	Size	Gzip	Brotli
createApp (CAPI only)	46.4 kB	18.2 kB	16.6 kB
createApp	54.4 kB	21.2 kB	19.4 kB
createSSRApp	58.6 kB	22.9 kB	20.9 kB
defineCustomElement	59.2 kB (+16 B)	22.7 kB (+2 B)	20.7 kB (-6 B)
overall	68.5 kB	26.4 kB	24 kB

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commit: 7f66fe6