定义

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

自定义 hook 的优势
。复用代码，让 setup 中的逻辑更清楚易懂

使用

首先我们做一个功能，鼠标点击屏幕，获取坐标

<template>
  <h2>当前鼠标的坐标是：x:{{ point.x }}，y:{{ point.y }}</h2>
</template>

<script>
import {onMounted, onBeforeUnmount,reactive} from 'vue'

export default {
  name: 'Demo',
  setup() {
    let point = reactive({
      x: 0,
      y: 0
    })

    function savePoint(event) {
      point.x = event.pageX;
      point.y = event.pageY;
    }
    onMounted(() => {
      window.addEventListener("click",savePoint)
    })

    onBeforeUnmount(()=>{
      window.removeEventListener("click",savePoint)
    })

    return {
      point,
    }
  },
}
</script>

然后改用使用 hooks，在 src 下新建 hooks 文件夹，增加 usePoint.js

import {onBeforeUnmount, onMounted, reactive} from "vue/dist/vue";

function savePoint() {
    let point = reactive({
        x: 0,
        y: 0
    })

    function savePoint(event) {
        point.x = event.pageX;
        point.y = event.pageY;
    }
    onMounted(() => {
        window.addEventListener("click",savePoint)
    })

    onBeforeUnmount(()=>{
        window.removeEventListener("click",savePoint)
    })
    return point
}

export default savePoint;

或者简写：

......
export default function() {
    ......
}

在 Demo.vue 中使用

<template>
  <h2>当前鼠标的坐标是：x:{{ point.x }}，y:{{ point.y }}</h2>
</template>

<script>
import usePoint from "@/hooks/usePoint";

export default {
  name: 'Demo',
  setup() {
    let point = usePoint()

    return {
      point
    }
  },
}
</script>

封装发ajax请求的hook函数（ts版本）

hooks 下新建 useRequest.ts

由于用到了 axios，所以安装axios：npm install axios

import {ref} from "vue";
import axios from "axios";

export default function <T>(url: string) {
    const loading = ref(true);
    const data = ref<T | null>(null);
    const errorMsg = ref('');

    axios.get(url).then(response => {
        loading.value = false
        data.value = response.data
    }).catch(error => {
        loading.value = false
        errorMsg.value = error.message || '未知错误'
    })

    return {
        loading,
        data,
        errorMsg
    }
}

App.vue

<template>
  <h3 v-if="loading">加载中...</h3>
  <h3 v-else-if="errorMsg">错误信息：{{errorMsg}}</h3>
  <!-- 对象 -->
  <ul v-else>
    <li>{{data.name}}</li>
    <li>{{data.address}}</li>
    <li>{{data.distance}}</li>
  </ul>
  <!-- 数组 -->
  <ul v-for="item in data" :key="item.name">
    <li>{{item.name}}</li>
    <li>{{item.address}}</li>
    <li>{{item.distance}}</li>
  </ul>
</template>

<script lang="ts">
import {defineComponent, watch} from 'vue';
import useRequest from "@/hooks/useRequest";

export default defineComponent({
  setup() {
    // 定义接口
    interface IAddress{
      name:string,
      address:string,
      distance:string
    }

    //const {loading,data,errorMsg} = useRequest<IAddress>("./address.json")//获取对象数据
    const {loading,data,errorMsg} = useRequest<IAddress[]>("./addressList.json")//获取对象数据
    watch(data, () => {
      if (data.value) {
        console.log(data.value.length)
      }
    })
    return {
      loading,
      data,
      errorMsg
    }
  }
});
</script>

测试数据有对象类型的 address.json

{
  "name": "家",
  "address": "开发区人民路22号",
  "distance": "100km"
}

还有数组类型的 addressList.json

[ {
  "name": "家",
  "address": "开发区人民路22号",
  "distance": "100km"
  },
  {
    "name": "公司",
    "address": "海港区建国路01号",
    "distance": "3km"
  }
]