vue3-watchEffect.vue

<script setup>
import { ref, watchEffect } from 'vue'

const number = ref(0);
const unwatch = watchEffect((onCleanup) => {
  const id = setInterval(() => {
    number.value++;
  }, 1000);
  
  onCleanup(() => clearInterval(id));
})

</script>

<template>
  <h1>{{ number }}</h1>
  <input v-model="number">
  <input type="button" @click="unwatch" value="unwatch" />
</template>