Handle Teleport SSR Hydration Carefully

Impact: HIGH - Teleports require special handling during SSR. The teleported content is not part of the server-rendered HTML string, causing hydration mismatches that can break the application or cause content to disappear.

This is a critical issue for Nuxt, Quasar SSR, and custom Vue SSR setups.

Task Checklist

• [ ] Wrap Teleport in <ClientOnly> component (Nuxt) for client-only rendering
• [ ] Use conditional rendering based on mount state for non-Nuxt SSR
• [ ] Use data-allow-mismatch attribute in Vue 3.5+ when intentional
• [ ] Test SSR applications thoroughly for hydration issues

Problem - SSR Hydration Mismatch:

<template>
  <!-- Server renders nothing for teleported content -->
  <!-- Client expects teleported content at #modals -->
  <!-- = Hydration mismatch -->
  <Teleport to="#modals">
    <div v-if="showModal" class="modal">
      Modal content
    </div>
  </Teleport>
</template>

Common error messages:

[Vue warn]: Hydration children mismatch in <div>:
server rendered element contains fewer child nodes than client vdom.

Solution 1 - Nuxt ClientOnly:

<template>
  <button @click="showModal = true">Open Modal</button>

  <!-- Only render on client, avoiding SSR -->
  <ClientOnly>
    <Teleport to="body">
      <div v-if="showModal" class="modal">
        Modal content
      </div>
    </Teleport>
  </ClientOnly>
</template>

Solution 2 - Manual Client Detection:

<template>
  <button @click="showModal = true">Open Modal</button>

  <!-- Only render after component mounts on client -->
  <Teleport v-if="isMounted" to="body">
    <div v-if="showModal" class="modal">
      Modal content
    </div>
  </Teleport>
</template>

<script setup>
import { ref, onMounted } from 'vue'

const showModal = ref(false)
const isMounted = ref(false)

onMounted(() => {
  isMounted.value = true
})
</script>

Solution 3 - Vue 3.5+ data-allow-mismatch:

<template>
  <!-- Suppress hydration warnings for intentional mismatches -->
  <div data-allow-mismatch>
    <Teleport to="body">
      <div v-if="showModal" class="modal">
        Modal content
      </div>
    </Teleport>
  </div>
</template>

SSR with Multiple Teleports

Multiple teleports to the same target can cause additional hydration issues:

<!-- Parent.vue -->
<template>
  <!-- First teleport -->
  <Teleport to="#modals">
    <NotificationBanner />
  </Teleport>

  <ChildComponent />
</template>

<!-- ChildComponent.vue -->
<template>
  <!-- Second teleport to same target - order matters! -->
  <Teleport to="#modals">
    <Modal />
  </Teleport>
</template>

For SSR, ensure consistent ordering or wrap each in ClientOnly.

Element Plus and UI Library SSR

Many UI libraries use Teleport internally. Element Plus components that use Teleport include:

• ElDialog
• ElDrawer
• ElTooltip
• ElDropdown
• ElSelect
• ElDatePicker

<template>
  <!-- These need special SSR handling -->
  <ClientOnly>
    <ElDialog v-model="visible">
      Dialog content
    </ElDialog>
  </ClientOnly>
</template>

Known Vue Issues

• Disabled teleports in fragments can cause hydration mismatches (Vue issue #6152)
• Nested teleports may cause app to break on hydration (Vue issue #5242)

Reference

• Vue.js SSR - Teleports
• Element Plus SSR Guide
• Nuxt ClientOnly Component