5 - watch family

[AlvinWang627]

<script setup lang="ts">
import { ref, watch } from 'vue'

const count = ref(0)

/**
 * Challenge 1: Watch once
 * Make sure the watch callback is only triggered once
 */
watch(
  count,
  () => {
    console.log('Only triggered once')
  },
  {
    once: true
  }
)
//The new watch option in vue3.4 [Once Watchers](https://vuejs.org/guide/essentials/watchers.html#once-watchers)
count.value = 1
setTimeout(() => (count.value = 2))

/**
 * Challenges 2: Watch object
 * Make sure the watch callback is triggered
 */
const state = ref({
  count: 0
})

watch(
  state,
  () => {
    console.log('The state.count updated')
  },
  {
    deep: true
  }
)

state.value.count = 2

/**
 * Challenge 3: Callback Flush Timing
 * Make sure visited the updated eleRef
 */

const eleRef = ref()
const age = ref(2)
watch(
  age,
  () => {
    console.log(eleRef.value)
  },
  {
    flush: 'post'
  }
)
age.value = 18
</script>

<template>
  <div>
    <p>
      {{ count }}
    </p>
    <p ref="eleRef">
      {{ age }}
    </p>
  </div>
</template>