How to set up Vue 3 parent component to emit event to child component

Question

I am attempting to set up a button in a Vue 3 Tailwind parent component to trigger a HeadlessUI transition event in a child component. My goal is to enable the button in the parent to emit an event, while the child component "watches" for the event before triggering the transition event as part of the callback function in the watch. So far, I have the parent component set up to trigger the emit, while the child component is set up to watch for the "transition" event. However, the event is not being executed. I'm afraid I don't have the watch in the child component set up correctly, so as to watch for the button click in the parent component. How can I go about enabling the child component to watch for the click of the button in the parent component?

Here is my code so far:

Parent:

<!-- This example requires Tailwind CSS v2.0+ -->
<template>
  <div class="min-h-full">
    <Disclosure as="nav" class="bg-gray-800">
      <div class="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8">
        <div class="flex items-center justify-between h-16">
          <div class="flex items-center">
            <div class="hidden md:block">
              <div class="ml-10 flex items-baseline space-x-4">
                <button type="button" @click="transition" class="text-white bg-blue-700 hover:bg-blue-800 focus:ring-4 focus:ring-blue-300 font-medium rounded-lg text-sm px-5 py-2.5 dark:bg-blue-600 dark:hover:bg-blue-700 focus:outline-none dark:focus:ring-blue-800">Click to transition</button>
              </div>
            </div>
          </div>
        </div>
      </div>
    </Disclosure>

    <main>
      <div class="max-w-7xl mx-auto py-6 sm:px-6 lg:px-8">
        <div class="px-4 py-6 sm:px-0">
          <HelloWorld :event="transition" />
        </div>
      </div>
    </main>
  </div>
</template>

<script setup>
import { Disclosure, DisclosureButton, DisclosurePanel, Menu, MenuButton, MenuItem, MenuItems } from '@headlessui/vue'
import { BellIcon, MenuIcon, XIcon } from '@heroicons/vue/outline'
import HelloWorld from './components/HelloWorld.vue'
</script>

Child:

<template>
  <div class="flex flex-col items-center py-16">
    <div class="w-96 h-96">
      <TransitionRoot
        appear
        :show="isShowing"
        as="template"
        enter="transform transition duration-[400ms]"
        enter-from="opacity-0 rotate-[-120deg] scale-50"
        enter-to="opacity-100 rotate-0 scale-100"
        leave="transform duration-200 transition ease-in-out"
        leave-from="opacity-100 rotate-0 scale-100 "
        leave-to="opacity-0 scale-95 "
      >
        <div class="w-full h-full bg-gray-400 rounded-md shadow-lg" />
      </TransitionRoot>
    </div>
  </div>
</template>

<script setup>
import { ref, toRefs, watch } from 'vue'
import { TransitionRoot } from '@headlessui/vue'

const props = defineProps({
  transition: Function
})
const { transition } = toRefs(props)
const isShowing = ref(true)

watch(transition, () => {
  isShowing.value = false

  setTimeout(() => {
    isShowing.value = true
  }, 500)
})
</script>

Answer 1

events should go up and state should go down.

make your child component to watch a property and the button in parent should change the state of that property

update:

const { transition } = toRefs(props)

you might be losing reactivity here.

more info: https://stackoverflow.com/a/64926664/420096

update2:

the way you made it should work, but point directly to the prop is fine too: https://codesandbox.io/s/relaxed-sea-y95x6c?file=/src/App.vue