除了 Vue 内置的一系列指令 (比如 v-model 或 v-show) 之外，Vue 还允许你注册自定义的指令 (Custom Directives)。

1. 生命周期钩子函数

一个自定义指令由一个包含类似组件生命周期钩子的对象来定义。钩子函数会接收到指令所绑定元素作为其参数。

在 <script setup> 中，任何以 v 开头的驼峰式命名的变量都可以被用作一个自定义指令。

<!-- App.vue -->
<template><div><button>切换</button><!-- 钩子函数里面都可以接受这些值myParam: 自定义参数；myModifier: 自定义修饰符 --><A v-move:myParam.myModifier="{ background: 'pink' }"></A></div>
</template><script setup lang="ts">
import { reactive, ref, Directive } from 'vue';
import A from './components/A.vue';
import B from './components/B.vue';
let flag = ref<boolean>(true)
const vMove: Directive = {created() {console.log('created')},beforeMount() {console.log('beforeMount')},mounted(...args: Array<any>) {console.log('mounted')console.log(args);},beforeUpdate() {console.log('beforeUpdate')},updated() {console.log('updated')},beforeUnmount() {console.log('beforeUnmount')},unmounted() {console.log('unmounted')}
}
</script><style scoped lang="less"></style>

• 0：该 div 元素。
• 1：传入的参数等。比如 arg 参数，modifiers 自定义修饰符，dir 目录，传入的 value 值，instance 组件实例。
• 2：当前组件的虚拟 DOM
• 3：上一个虚拟 DOM

<!-- App.vue -->
<template><div><button>切换</button><!-- 钩子函数里面都可以接受这些值myParam: 自定义参数；myModifier: 自定义修饰符 --><A v-move:myParam.myModifier="{ background: 'pink' }"></A></div>
</template><script setup lang="ts">
import { reactive, ref, Directive, DirectiveBinding } from 'vue';
import A from './components/A.vue';
import B from './components/B.vue';
let flag = ref<boolean>(true)
type Dir = {background: string;
}
const vMove: Directive = {created() {console.log('created')},beforeMount() {console.log('beforeMount')},mounted(el: HTMLElement, dir: DirectiveBinding<Dir>) {console.log('mounted')console.log(el);console.log(dir);el.style.background = dir.value.background;},// 传入的数据发生变化（比如此时的background）时触发 beforeUpdate 和 updatedbeforeUpdate() {console.log('beforeUpdate')},updated() {console.log('updated')},beforeUnmount() {console.log('beforeUnmount')},unmounted() {console.log('unmounted')}
}
</script><style scoped lang="less"></style>

2. 指令简写

<!-- App.vue -->
<template><div class="btns"><button v-has-show="123">创建</button><button>编辑</button><button>删除</button></div>
</template><script setup lang="ts">
import { reactive, ref, DirectiveBinding } from 'vue';
import type { Directive } from 'vue'
const vHasShow: Directive = (el, binding) => {console.log(el, binding) ;
}
</script><style scoped lang="less">
.btns {button {margin: 10px;}
}
</style>

应用场景1：按钮鉴权

根据能否从 localStorage（或者后台返回） 中获取数据，来判断是否显示某个按钮。

<!-- App.vue -->
<template><div class="btns"><button v-has-show="'shop:create'">创建</button><button v-has-show="'shop:edit'">编辑</button><button v-has-show="'shop:delete'">删除</button></div>
</template><script setup lang="ts">
import { reactive, ref, DirectiveBinding } from 'vue';
import type { Directive } from 'vue'
localStorage.setItem('userId', 'xiuxiu')
// mock 后台返回的数据
const permissions = ['xiuxiu:shop:create',// 'xiuxiu:shop:edit',  // 后台没有相应数据，则不显示该对应的按钮'xiuxiu:shop:delete'
]
const userId = localStorage.getItem('userId') as string
const vHasShow: Directive = (el, binding) => {if(!permissions.includes(userId + ':' + binding.value)) {el.style.display = 'none'}
}
</script><style scoped lang="less">
.btns {button {margin: 10px;}
}
</style>

应用场景2：鼠标拖拽

拖拽粉色框移动大盒子。

<!-- App.vue -->
<template><div v-move class="box"><div class="header"></div><div>内容</div></div>
</template><script setup lang="ts">
import { Directive, DirectiveBinding } from 'vue';const vMove:Directive<any,void> = (el:HTMLElement, binding:DirectiveBinding)=> {let moveElement:HTMLElement = el.firstElementChild as HTMLElement;console.log(moveElement);const mouseDown = (e:MouseEvent) => {// 记录原始位置// clientX 鼠标点击位置的X轴坐标// clientY 鼠标点击位置的Y轴坐标// offsetLeft 鼠标点击的子元素距离其父元素的左边的距离// offsetTop 鼠标点击的子元素距离其父元素的顶部的距离let X = e.clientX - el.offsetLeft;let Y = e.clientY - el.offsetTop;const move = (e:MouseEvent) => {console.log(e);el.style.left = e.clientX - X + 'px';el.style.top = e.clientY - Y + 'px';}document.addEventListener('mousemove', move);document.addEventListener('mouseup', () => {document.removeEventListener('mousemove', move);})}moveElement.addEventListener('mousedown', mouseDown);
}
</script><style scoped lang="less">
.box {position: fixed;height: 200px;width: 200px;top: 50%;left: 50%;transform: translate(-50%, -50%);border: 1px solid #000;.header {height: 50px;width: 100%;background: pink;border-bottom: #000 1px solid;}
}
</style>

应用场景3：懒加载

let imageList = import.meta.glob('./assets/images/*.*', { eager: true })

let imageList = import.meta.glob('./assets/images/*.*')

 // 判断图片是否在可视区const observer = new IntersectionObserver((e)=> {console.log(e[0]);})  // 监听元素observer.observe(el)

<!-- App.vue -->
<template><div><div><img v-lazy="item" width="400" height="500" v-for="item in arr" alt=""></div></div>
</template><script setup lang="ts">
import { Directive, DirectiveBinding } from 'vue';let imageList:Record<string,{default:string}> = import.meta.glob('./assets/images/*.*', { eager: true })
let arr = Object.values(imageList).map(item=>item.default)
console.log(arr);
let vLazy:Directive<HTMLImageElement,string> = async (el,binding)=> {const def = await import('./assets/pinia.svg')el.src = def.default// 判断图片是否在可视区const observer = new IntersectionObserver((e)=> {console.log(e[0],binding.value);if(e[0].intersectionRatio > 0) {setTimeout(()=> {el.src = binding.value},2000)observer.unobserve(el)}})  // 监听元素observer.observe(el)
}
</script><style scoped lang="less"></style>

1. 进入可视区比例 > 0：

   

2. 过 2s ，替换图片