Michael Hoffmann LogoMichael Hoffmann
·
2 min read

Vue Tip: Check if Slot Is Empty

Vue Tip: Check if Slot Is Empty Image
TemplateScriptSlots

You can check if a slot is empty, for example, only to render it if it is available or has content.

Check if a slot is empty

To check if a slot is empty, you can use $slots, an object representing the slots passed by the parent component.

Each slot is exposed on $slots as a function that returns an array of vnodes under the key corresponding to that slot's name. The default slot is exposed as $slots.default.

If a slot is a scoped slot, arguments passed to the slot functions are available to the slot as its slot props.

In the following example, the footer is only rendered if the slot with the name footer is present:

<template> <footer v-if="$slots.footer"> <h3>My Footer Heading</h3> <slot name="footer" /> </footer> </template>

Vue 2 Code

Of course, you can use that functionality in Vue 2 as well:

<template> <footer v-if="showFooter"> <h3>My Footer Heading</h3> <slot name="footer" /> </footer> </template> <script> export default { data() { return { showFooter: false, } }, created() { this.setShowSlots() }, beforeUpdate() { this.setShowSlots() }, methods: { setShowSlots() { this.showFooter = this.$slots.footer?.[0] }, }, } </script>

useSlots composable

Usage of slots inside <script setup> should be relatively rare since you can directly access them as $slots in the template. In the rare case where you need them, you can use the useSlots composable:

<template> <footer v-if="showFooter"> <h3>My Footer Heading</h3> <slot name="footer" /> </footer> </template> <script setup> import { useSlots } from 'vue' const slots = useSlots() const showFooter = () => { return !!slots.footer } </script>

Info

useSlots is a runtime function that returns the equivalent of setupContext.slots. You can use it in normal Composition API functions as well.

Check if a slot has content

In some cases, you probably want to check if the slot is not empty and has content inside.

You can do that by checking the array of vnodes, if they are empty or not:

<script setup lang="ts"> import type { Slot, VNode } from 'vue' import { Comment, computed, Fragment, useSlots } from 'vue' const slots = useSlots() function isSlotAvailable() { return !!slots?.footer } // Adapted from https://github.com/vuejs/vue-next/blob/ca17162e377e0a0bf3fae9d92d0fdcb32084a9fe/packages/runtime-core/src/helpers/renderSlot.ts#L77 const isVnodeEmpty = (vnodes: Array<VNode>) => { return vnodes.every((node: VNode) => { if (node.type === Comment) { return true } if (node.type === Text && typeof node.children === 'string' && !node.children.trim()) { return true } if ( node.type === Fragment && isVnodeEmpty(node.children as Array<VNode>) ) { return true } return false }) } const hasSlotContent = (slot: Slot<any> | undefined) => { if (!slot) { return false } return !isVnodeEmpty(slot()) } </script> <template> <div class="container"> <h3>Hello World</h3> <span>isSlotAvailable: {{ isSlotAvailable() }}</span> <span>hasSlotContent: {{ hasSlotContent(slots?.footer) }}</span> <footer v-if="slots.footer"> <h3>My Footer Heading</h3> <slot name="footer" /> </footer> </div> </template>

StackBlitz

The code for this tip is interactively available in the following StackBlitz project:

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