什么是hooks? ———本质是一个函数, 把setup函数中使用的Composition API进行了封装, 类似于vue2.x中的mixin.

自定义hooks的优势: 复用代码, 让setup中国呢的逻辑更清楚易懂.

示例代码:
useSum.ts中内容如下:

import {ref,onMounted} from 'vue'

export default function(){
  let sum = ref(0)

  const increment = ()=>{
    sum.value += 1
  }
  const decrement = ()=>{
    sum.value -= 1
  }
  onMounted(()=>{
    increment()
  })

  //向外部暴露数据
  return {sum,increment,decrement}
}		

useDog.ts中内容如下:

import {reactive,onMounted} from 'vue'
import axios,{AxiosError} from 'axios'

export default function(){
  let dogList = reactive<string[]>([])

  // 方法
  async function getDog(){
    try {
      // 发请求
      let {data} = await axios.get('https://dog.ceo/api/breed/pembroke/images/random')
      // 维护数据
      dogList.push(data.message)
    } catch (error) {
      // 处理错误
      const err = <AxiosError>error
      console.log(err.message)
    }
  }

  // 挂载钩子
  onMounted(()=>{
    getDog()
  })
	
  //向外部暴露数据
  return {dogList,getDog}
}

组件中具体使用:

<template>
  <h2>当前求和为：{{sum}}</h2>
  <button @click="increment">点我+1</button>
  <button @click="decrement">点我-1</button>
  <hr>
  <img v-for="(u,index) in dogList.urlList" :key="index" :src="(u as string)"> 
  <span v-show="dogList.isLoading">加载中......</span><br>
  <button @click="getDog">再来一只狗</button>
</template>

<script lang="ts">
  import {defineComponent} from 'vue'

  export default defineComponent({
    name:'App',
  })
</script>

<script setup lang="ts">
  import useSum from './hooks/useSum'
  import useDog from './hooks/useDog'
	
  let {sum,increment,decrement} = useSum()
  let {dogList,getDog} = useDog()
</script>