我就廢話不多說了，大家還是直接看代碼吧~

export default { data() { return { item: ’’ } }, watch: { item(now, before){ let remove = before.filter(x => now.indexOf(x) == -1); let add = now.filter(x => before.indexOf(x) == -1); /* 顯示字符串或數組元素的增加和減少 */ console.log(add, remove); } }}

補充知識：Vuejs+Element監聽-window.resize-el-menu響應式顯示

效果

代碼

template

<template> <div class='sidebar'> <!-- 折疊按鈕 --> <div @click='collapseChage'> <i v-show='!collapse'> &nbsp;&nbsp; <small>收縮側邊欄</small> </i> <i v-show='collapse'></i> </div> <el-menu :default-active='onRoutes' :collapse='collapse' text-color='#8d9199' active-text-color='#20a0ff' unique-opened router > <template v-for='item in items'> <template v-if='item.subs'> <el-submenu :index='item.index' :key='item.index'> <template slot='title'> <i :class='item.icon'></i> <span slot='title'>{{ item.title }}</span> </template> <template v-for='subItem in item.subs'> <el-submenu v-if='subItem.subs' :index='subItem.index' :key='subItem.index'> <template slot='title'> <i :class='subItem.icon'></i> {{ subItem.title }} </template> <el-menu-item v-for='(threeItem,i) in subItem.subs' :key='i' :index='threeItem.index' >{{ threeItem.title }}</el-menu-item> </el-submenu> <el-menu-item v-else :index='subItem.index' :key='subItem.index'> <i :class='subItem.icon'></i> {{ subItem.title }} </el-menu-item> </template> </el-submenu> </template> <template v-else> <el-menu-item :index='item.index' :key='item.index'> <i :class='item.icon'></i> <span slot='title'>{{ item.title }}</span> </el-menu-item> </template> </template> </el-menu> <div> <i v-show='collapse'></i> </div> </div></template>

javascript

<script>import bus from './bus';import { menu } from '../../data/menu';export default { data() { return { collapse: false, items: menu, screenWidth: 1000 }; }, computed: { onRoutes() { return this.$route.path.replace('/', ''); } }, created() { // 通過 Event Bus 進行組件間通信，來折疊側邊欄 bus.$on('collapse', msg => { this.collapse = msg; }); }, mounted() { // if (document.body.clientWidth < 1500) { // this.collapseChage(); // } const that = this; window.addEventListener('resize', function() { return (() => { window.screenWidth = document.body.clientWidth; that.screenWidth = window.screenWidth; })(); }); }, watch: { screenWidth(val) { if (!this.timer) { this.screenWidth = val; this.timer = true; let that = this; setTimeout(function() { // that.screenWidth = that.$store.state.canvasWidth console.log(that.screenWidth); that.auto(); that.timer = false; }, 400); } } }, methods: { // 側邊欄折疊 collapseChage() { this.collapse = !this.collapse; bus.$emit('collapse', this.collapse); }, auto() { if (this.screenWidth < 1200) { console.log('收起來'); this.collapse = true; bus.$emit('collapse', true); } else { console.log('展開'); this.collapse = false; bus.$emit('collapse', false); } } }};</script>

css

<style scoped>.sidebar { z-index: 1024; display: block; position: fixed; left: 0; top: 70px; bottom: 0; overflow-y: scroll;}.sidebar::-webkit-scrollbar { width: 0;}.sidebar-el-menu:not(.el-menu--collapse) { width: 200px;}.sidebar > ul { height: 100%; /*寫給不支持calc()的瀏覽器*/ height: calc(100% - 52px); top: 30px; background-color: rgb(235, 239, 243); border-top: 1px solid #d6d6d6;}.sidebar > ul > li,.sidebar > ul > li div { background-color: rgb(235, 239, 243);}.sidebar > ul > li > ul { background-color: rgb(235, 239, 243);}.el-menu { background-color: rgb(235, 239, 243);}i { margin-right: 10px;}.collapse-btn { height: 30px; width: 100%; cursor: pointer; line-height: 30px; position: absolute; top: 0; left: 0; background-color: #f4f6fa; color: #fff; text-align: center; overflow: hidden; box-sizing: border-box; box-shadow: 0 5px 10px #ddd;}.collapse-btn i { color: #8d9199; padding: 1px; cursor: pointer; overflow: hidden; text-overflow: ellipsis;}/* .collapse-btn:before{ content: ''; display: block; height: 0; border-top: 1px dotted #909399; position: absolute; left: 15px; right: 15px; top: 18px; } */</style>

##注意⚠️

此開發框架是github 名為 lin-xin 的 vue-manage-system

因公司項目需要兼容iPad，故而修改

詳細代碼點擊這里

以上這篇Vue 監聽元素前后變化值實例就是小編分享給大家的全部內容了，希望能給大家一個參考，也希望大家多多支持好吧啦網。