Vue 3: computed

App.vue

<template>
  <div>
    <input v-model.lazy="name" />
    <p>{{ msg }}</p>
  </div>
</template>

<script>
import { reactive, toRefs, computed  } from "vue";

export default {
  setup () {

    const data = reactive({
      name: 'Guillaume',
      msg: computed(() => { 
        return `Hello ${data.name}`
      })
    })

    return {
      ...toRefs(data)
    }
  }
}
</script>