agent-skills/skills/vue-best-practices/reference/slot-fallback-content-default-values.md

title, impact, impactDescription, type, tags

title	impact	impactDescription	type	tags
Provide Fallback Content for Slots	LOW	Components without slot fallbacks may render empty or broken when content is not provided	best-practice	vue3 slots fallback-content component-design reusability

Provide Fallback Content for Slots

Impact: LOW - Providing sensible default content inside <slot> elements makes components more resilient and user-friendly. Fallback content renders when no slot content is provided by the parent.

Task Checklist

• Add fallback content inside slot elements for optional slots
• Use meaningful defaults that make sense standalone
• Consider i18n for text fallbacks in internationalized apps
• Document which slots have fallbacks and what they display

Without Fallback (fragile):

<!-- SubmitButton.vue -->
<template>
  <button type="submit" class="btn-primary">
    <!-- Empty if no content provided -->
    <slot></slot>
  </button>
</template>

<!-- Usage without content - renders empty button -->
<SubmitButton />
<!-- Result: <button type="submit" class="btn-primary"></button> -->

With Fallback (resilient):

<!-- SubmitButton.vue -->
<template>
  <button type="submit" class="btn-primary">
    <slot>Submit</slot>
  </button>
</template>

<!-- Usage without content - shows default -->
<SubmitButton />
<!-- Result: <button type="submit" class="btn-primary">Submit</button> -->

<!-- Usage with content - overrides default -->
<SubmitButton>Save Changes</SubmitButton>
<!-- Result: <button type="submit" class="btn-primary">Save Changes</button> -->

Named Slots with Fallbacks

<!-- Card.vue -->
<template>
  <div class="card">
    <header class="card-header">
      <slot name="header">
        <h3>Card Title</h3>
      </slot>
    </header>

    <main class="card-body">
      <slot>
        <p>No content provided.</p>
      </slot>
    </main>

    <footer class="card-footer">
      <slot name="footer">
        <button>Close</button>
      </slot>
    </footer>
  </div>
</template>

Complex Fallback Content

Fallback content can include multiple elements and logic:

<!-- UserAvatar.vue -->
<template>
  <div class="avatar-container">
    <slot name="image">
      <!-- Complex fallback with conditional logic -->
      <img
        v-if="user?.avatar"
        :src="user.avatar"
        :alt="user.name"
      />
      <div v-else class="avatar-placeholder">
        {{ initials }}
      </div>
    </slot>
  </div>
</template>

<script setup>
import { computed } from 'vue'

const props = defineProps({
  user: Object
})

const initials = computed(() => {
  if (!props.user?.name) return '?'
  return props.user.name
    .split(' ')
    .map(n => n[0])
    .join('')
    .toUpperCase()
})
</script>

When to Use Fallbacks

Slot Purpose	Fallback Recommended?	Example
Button text	Yes	"Submit", "Click here"
Icon slot	Yes	Default icon component
Modal title	Yes	"Dialog"
Required content area	No	Main content slot
Customization only	Optional	Action buttons slot

Reference

• Vue.js Slots - Fallback Content