vue3 computed typeScript

<template>
  <div>
    <input type="text" v-model="firstName">
    <input type="text" v-model="lastName">
    <p>{{ firstName }} --- {{ lastName }}</p>
    <p>name:{{ name }}</p>
  </div>

  <div>
    <button @click="change">修改</button>
  </div>
</template>
<script setup lang="ts">
import {computed, ref} from "vue";

let firstName = ref("");
let lastName = ref("");

const name = computed({
  get() {
    return firstName.value + " " + lastName.value
  },
  set(value) {

    firstName.value + lastName.value

  }
})


</script>