From f41d16e6c73b2d8133563ae9c80cafb11ef17a51 Mon Sep 17 00:00:00 2001
From: daiwei <daiwei521@126.com>
Date: Sat, 4 Oct 2025 10:52:21 +0800
Subject: [PATCH 1/3] fix(custom-element): optimize slot retrieval to avoid
 duplicates

---
 packages/runtime-dom/src/apiCustomElement.ts | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/packages/runtime-dom/src/apiCustomElement.ts b/packages/runtime-dom/src/apiCustomElement.ts
index 6b1c8f0cae8..6c6ab395e04 100644
--- a/packages/runtime-dom/src/apiCustomElement.ts
+++ b/packages/runtime-dom/src/apiCustomElement.ts
@@ -685,11 +685,23 @@ export class VueElement
     if (this._teleportTargets) {
       roots.push(...this._teleportTargets)
     }
-    return roots.reduce<HTMLSlotElement[]>((res, i) => {
-      res.push(...Array.from(i.querySelectorAll('slot')))
-      return res
-    }, [])
+
+    const seen = new Set<HTMLSlotElement>()
+    const slots: HTMLSlotElement[] = []
+    for (const root of roots) {
+      const found = root.querySelectorAll<HTMLSlotElement>('slot')
+      for (let i = 0; i < found.length; i++) {
+        const slot = found[i]
+        if (!seen.has(slot)) {
+          seen.add(slot)
+          slots.push(slot)
+        }
+      }
+    }
+
+    return slots
   }
+
   /**
    * @internal
    */

From b661cd340281e277da3f32d1f3fff2fbb5a18509 Mon Sep 17 00:00:00 2001
From: daiwei <daiwei521@126.com>
Date: Sat, 4 Oct 2025 11:02:41 +0800
Subject: [PATCH 2/3] test: add test

---
 .../__tests__/customElement.spec.ts           | 38 +++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/packages/runtime-dom/__tests__/customElement.spec.ts b/packages/runtime-dom/__tests__/customElement.spec.ts
index 36c9e918c9a..3e48edffe6d 100644
--- a/packages/runtime-dom/__tests__/customElement.spec.ts
+++ b/packages/runtime-dom/__tests__/customElement.spec.ts
@@ -1430,6 +1430,44 @@ describe('defineCustomElement', () => {
       app.unmount()
     })
 
+    test('teleport target is ancestor of custom element host', async () => {
+      const Child = defineCustomElement(
+        {
+          render() {
+            return [
+              h(Teleport, { to: '#t1' }, [renderSlot(this.$slots, 'header')]),
+            ]
+          },
+        },
+        { shadowRoot: false },
+      )
+      customElements.define('my-el-teleport-child-target', Child)
+
+      const App = {
+        render() {
+          return h('div', { id: 't1' }, [
+            h('my-el-teleport-child-target', null, {
+              default: () => [h('div', { slot: 'header' }, 'header')],
+            }),
+          ])
+        },
+      }
+      const app = createApp(App)
+      app.mount(container)
+
+      const target1 = document.getElementById('t1')!
+      expect(target1.outerHTML).toBe(
+        `<div id="t1">` +
+          `<my-el-teleport-child-target data-v-app="">` +
+          `<!--teleport start--><!--teleport end-->` +
+          `</my-el-teleport-child-target>` +
+          `<div slot="header">header</div>` +
+          `</div>`,
+      )
+
+      app.unmount()
+    })
+
     test('toggle nested custom element with shadowRoot: false', async () => {
       customElements.define(
         'my-el-child-shadow-false',

From 72b5019416168b674d6459b89befe0a26d1ed6c1 Mon Sep 17 00:00:00 2001
From: daiwei <daiwei521@126.com>
Date: Sat, 4 Oct 2025 16:57:20 +0800
Subject: [PATCH 3/3] chore: tweaks

---
 packages/runtime-dom/src/apiCustomElement.ts | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/packages/runtime-dom/src/apiCustomElement.ts b/packages/runtime-dom/src/apiCustomElement.ts
index 6c6ab395e04..912523cb410 100644
--- a/packages/runtime-dom/src/apiCustomElement.ts
+++ b/packages/runtime-dom/src/apiCustomElement.ts
@@ -686,20 +686,15 @@ export class VueElement
       roots.push(...this._teleportTargets)
     }
 
-    const seen = new Set<HTMLSlotElement>()
-    const slots: HTMLSlotElement[] = []
+    const slots = new Set<HTMLSlotElement>()
     for (const root of roots) {
       const found = root.querySelectorAll<HTMLSlotElement>('slot')
       for (let i = 0; i < found.length; i++) {
-        const slot = found[i]
-        if (!seen.has(slot)) {
-          seen.add(slot)
-          slots.push(slot)
-        }
+        slots.add(found[i])
       }
     }
 
-    return slots
+    return Array.from(slots)
   }
 
   /**