分享12个Vue开发中的性能优化小技巧(实用!)

export default {
 data: () => ({
   userList: []
}),
 async created() {
   const users = await axios.get("/api/users");
   this.userList = Object.freeze(users);
}
};

export function defineReactive (...){
   const property = Object.getOwnPropertyDescriptor(obj, key)
   if (property && property.configurable === false) {
       return
  }
   ...
}

<recycle-scroller
 class="items"
 :items="items"
 :item-size="24"
>
 <template v-slot="{ item }">
   <FetchItemView
     :item="item"
     @vote="voteItem(item)"
   />
 </template>
</recycle-scroller>

<template>
   <ul>
     <li v-for="item in activeList" :key="item.id">
      {{ item.title }}
     </li>
   </ul>
</template>
<script>
// Vue2.x
export default {
   computed: {
     activeList() {
       return this.list.filter( item => {
         return item.isActive
      })
    }
  }
}

// Vue3
import { computed } from "vue";
const activeList = computed(() => {
 return list.filter( item => {
   return item.isActive
})
})
</script>

<template>
 <div>
   <div v-show="status" class="on">
     <my-components />
   </div>
   <section v-show="!status" class="off">
     <my-components >
   </section>
 </div>
</template>

<template functional>
 <div>
   <div class="content">{{ value }}</div>
 </div>
</template>
<script>
export default {
 props: ['value']
}
</script>

// 或者
Vue.component('my-component', {
 functional: true, // 表示该组件为函数式组件
 props: { ... }, // 可选
 // 第二个参数为上下文，没有 this
 render: function (createElement, context) {
   // ...
}
})

<template>
 <div :style="{ opacity: number / 100 }">
   <div>{{ someThing() }}</div>
 </div>
</template>
<script>
export default {
 props:['number'],
 methods: {
   someThing () { /* 耗时任务 */ }
}
}
</script>

<template>
<div>  
 <my-child />
</div>
</template>
<script>
export default {
components: {  
 MyChild: {  
  methods: {    
   someThing () { /* 耗时任务 */ }    
  },   
   render (h) {  
    return h('div', this.someThing())  
  } 
 }
}
}
</script>

<template> 
 <div :style="{ opacity: number / 100 }"> {{ result
}}</div>
</template>
<script>
import { someThing } from '@/utils'
export default {
 props: ['number'], 
 computed: {  
  base () { return 100 },  
  result () {   
   let base = this.base, number = this.number // 
保存起来    
  for (let i = 0; i < 1000; i++) {   
   number += someThing(base) // 避免频繁引用
this.xx   
  }   
   return number 
  }
}
}
</script>

// main.js
import Element3 from "plugins/element3";
Vue.use(Element3)

// element3.js
// 完整引入
import element3 from "element3";
import "element3/lib/theme-chalk/index.css";

// 按需引入
// import "element3/lib/theme-chalk/button.css";
// ...
// import { 
// ElButton, 
// ElRow, 
// ElCol, 
// ElMain, 
// .....
// } from "element3";

export default function (app) { 
// 完整引入 
app.use(element3)  

// 按需引入 
// app.use(ElButton);
}

import Home from '@/components/Home'
const router = new VueRouter({  
 routes: [  
  { path: '/home', component: Home }
]
})

const router = new VueRouter({
routes: [ 
 { path: '/home', component: () => 
import('@/components/Home') }, 
 { path: '/login', component: 
require('@/components/Home').default }
]
})

<template>
 <div id="app"> 
  <keep-alive>  
   <router-view/> 
  </keep-alive>
</div>
</template>

<script>
export default {  
 created() {   
  this.timer = setInterval(this.refresh, 2000)  
  addEventListener('touchmove', 
this.touchmove, false) 
 }, 
  beforeDestroy() {  
   clearInterval(this.timer)   
   this.timer = null   
   removeEventListener('touchmove', 
this.touchmove, false) 
 }
}
</script>

npm i vue-lazyload -S

// main.js
import VueLazyload from 'vue-lazyload'
Vue.use(VueLazyload)

// 接着就可以在页面中使用 v-lazy 懒加载图片了
<img v-lazy="/static/images/1.png">

const LazyLoad = { 
// install方法 
install(Vue, options) {  
 const defaultSrc = options.default 
 Vue.directive('lazy', {  
  bind(el, binding) {   
   LazyLoad.init(el, binding.value, defaultSrc) 
 },   
  inserted(el) {     
   if (IntersectionObserver) {    
    LazyLoad.observe(el)     
  } else {      
    LazyLoad.listenerScroll(el)    
  }  
 }, 
})
}, 
// 初始化 
init(el, val, def) { 
 el.setAttribute('data-src', val)  
 el.setAttribute('src', def)
}, 
// 利用IntersectionObserver监听el
observe(el) {  
 var io = new IntersectionObserver((entries) => {  
  const realSrc = el.dataset.src    
 if (entries[0].isIntersecting) {   
  if (realSrc) {      
   el.src = realSrc       
   el.removeAttribute('data-src')    
  }   
 } 
}) 
 io.observe(el)
}, 
// 监听scroll事件
listenerScroll(el) {  
 const handler =
LazyLoad.throttle(LazyLoad.load, 300) 
 LazyLoad.load(el)  
 window.addEventListener('scroll', () => {   
  handler(el) 
 })
}, 
// 加载真实图片 
load(el) {  
 const windowHeight =
document.documentElement.clientHeight
 const elTop = el.getBoundingClientRect().top  
 const elBtm = 
el.getBoundingClientRect().bottom 
 const realSrc = el.dataset.src  
 if (elTop - windowHeight < 0 && elBtm > 0) {  
  if (realSrc) {     
   el.src = realSrc    
   el.removeAttribute('data-src')  
  } 
 }
}, 
// 节流 
throttle(fn, delay) {  
 let timer  
 let prevTime  
 return function (...args) {   
  const currTime = Date.now() 
  const context = this    
  if (!prevTime) prevTime = currTime  
  clearTimeout(timer)   
  
  if (currTime - prevTime > delay) {     
   prevTime = currTime      
   fn.apply(context, args)    
   clearTimeout(timer)      
   return   
 }  

 timer = setTimeout(function () {   
  prevTime = Date.now()  
  timer = null   
  fn.apply(context, args)   
}, delay) 
}
},
}
export default LazyLoad

<img v-LazyLoad="xxx.jpg" />