slot插槽的显示使用

想实现的效果是如果有slot显示slot,没有则显示demo

<div>
    <div class="demo" v-if="!$slots.default"><div>
    <slot></slot>
</div>

或则

<template>
  <div>
     <div class="demo" v-if="isShow"></div>
     <slot></slot>
</div>
</template>

<script>
export default {
    computed: {
        isShow () {
            console.log(this.$slots)
            return this.$slots.default
        }
    }
}
</script>