charging-cabinet/software/h5-uniapp/.agents/skills/vue-best-practices/reference/slot-conditional-rendering-with-slots.md

title, impact, impactDescription, type, tags

title	impact	impactDescription	type	tags
Use $slots to Conditionally Render Slot Wrapper Elements	MEDIUM	Empty wrapper elements render in DOM when slots have no content, affecting layout and styling	best-practice	vue3 slots conditional-rendering performance dom-optimization

Use $slots to Conditionally Render Slot Wrapper Elements

Impact: MEDIUM - When building reusable components with optional slots, wrapper elements (divs, sections, etc.) will render even if no slot content is provided. This can cause layout issues, unnecessary DOM nodes, and styling problems. Use the $slots property to conditionally render wrappers only when slots have content.

Task Checklist

• Check $slots before rendering wrapper elements for optional slots
• Use v-if="$slots.slotName" to conditionally render wrappers
• Remember that $slots.default checks the default slot
• Keep DOM clean by avoiding empty wrapper elements

Incorrect:

<!-- Card.vue -->
<template>
  <div class="card">
    <!-- BAD: Header wrapper renders even with no content -->
    <div class="card-header">
      <slot name="header" />
    </div>

    <!-- BAD: Empty div with padding/margin affects layout -->
    <div class="card-body">
      <slot />
    </div>

    <!-- BAD: Footer renders as empty element -->
    <div class="card-footer">
      <slot name="footer" />
    </div>
  </div>
</template>

<style scoped>
.card-header { padding: 16px; border-bottom: 1px solid #eee; }
.card-footer { padding: 16px; border-top: 1px solid #eee; }
</style>

When used without all slots:

<!-- Results in empty .card-header and .card-footer divs with borders -->
<Card>
  <p>Just body content</p>
</Card>

Correct:

<!-- Card.vue -->
<template>
  <div class="card">
    <!-- GOOD: Only render header wrapper if slot has content -->
    <div v-if="$slots.header" class="card-header">
      <slot name="header" />
    </div>

    <!-- GOOD: Check default slot -->
    <div v-if="$slots.default" class="card-body">
      <slot />
    </div>

    <!-- GOOD: Footer only renders when provided -->
    <div v-if="$slots.footer" class="card-footer">
      <slot name="footer" />
    </div>
  </div>
</template>

<style scoped>
.card-header { padding: 16px; border-bottom: 1px solid #eee; }
.card-footer { padding: 16px; border-top: 1px solid #eee; }
</style>

Now clean DOM:

<!-- Only renders .card-body, no empty header/footer -->
<Card>
  <p>Just body content</p>
</Card>

Advanced: Using $slots in Script Setup

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

const slots = useSlots()

const hasHeader = computed(() => !!slots.header)
const hasFooter = computed(() => !!slots.footer)

// Can also check slot content conditionally in logic
function getLayoutClass() {
  if (slots.header && slots.footer) return 'full-layout'
  if (slots.header) return 'header-only'
  if (slots.footer) return 'footer-only'
  return 'minimal'
}
</script>

<template>
  <div :class="['card', getLayoutClass()]">
    <header v-if="hasHeader">
      <slot name="header" />
    </header>
    <main>
      <slot />
    </main>
    <footer v-if="hasFooter">
      <slot name="footer" />
    </footer>
  </div>
</template>

When to Use This Pattern

Scenario	Use $slots Check?
Wrapper has styling (padding, borders, background)	Yes
Wrapper affects layout (flex, grid)	Yes
Slot is always expected to have content	No
No wrapper element around slot	No
Wrapper is purely semantic (no visual impact)	Optional

Reference

• Vue.js Slots - Conditional Slots