vue3组合式api中怎么使用计算属性vue3组合式api中怎么使用计算属性，怎么在typescript中标注类型，看这

1.vue3组合式api中怎么使用计算属性

import { ref, computed } from 'vue'
const num1 = ref(1)
const num2 = ref(2)
const sum = computed(() => num1.value + num2.value)
// computed 返回的是一个ref

2.为 computed() 标注类型

import { ref, computed } from 'vue'
const num1 = ref(1)
const num2 = ref(2)
const sum = computed<number>(() => num1.value + num2.value)

3.创建一个可写的计算属性

import { ref, computed } from 'vue'
const num = ref(1)
const sum = computed({
  get: () => num.value + 1,
  set: (val) => {
    num.value = val -1
  }
})