通俗的来讲,computed被多次调用的时候,因为存在缓存特性,数据没有发生变化的时候,就会在缓存中查找计算值。发生变化之后又会重新执行computed。
DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Documenttitle>
<style>
table {
border: 1px solid #000;
text-align: center;
width: 300px;
}
th,
td {
border: 1px solid #000;
}
h3 {
position: relative;
}
span {
position: absolute;
left: 145px;
top: -4px;
width: 16px;
height: 16px;
color: white;
font-size: 12px;
text-align: center;
border-radius: 50%;
background-color: #e63f32;
}
style>
head>
<body>
<div id="app">
<h3>小黑的礼物清单<span>{{totalCount}}span>h3>
<h3>小黑的礼物清单<span>{{totalCount}}span>h3>
<h3>小黑的礼物清单<span>{{totalCount}}span>h3>
<h3>小黑的礼物清单<span>{{totalCount}}span>h3>
<h3>小黑的礼物清单<span>{{totalCountMethod()}}span>h3>
<h3>小黑的礼物清单<span>{{totalCountMethod()}}span>h3>
<h3>小黑的礼物清单<span>{{totalCountMethod()}}span>h3>
<h3>小黑的礼物清单<span>{{totalCountMethod()}}span>h3>
<table>
<tr>
<th>名字th>
<th>数量th>
tr>
<tr v-for="(item, index) in list" :key="item.id">
<td>{{ item.name }}td>
<td>{{ item.num }}个td>
tr>
table>
<p>礼物总数:{{ totalCount }} 个p>
div>
<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/vue.js">script>
<script>
const app = new Vue({
el: '#app',
data: {
// 现有的数据
list: [
{ id: 1, name: '篮球', num: 3 },
{ id: 2, name: '玩具', num: 2 },
{ id: 3, name: '铅笔', num: 5 },
]
},
methods: {
totalCountMethod() {
console.log("methods方法被执行了");
let total = this.list.reduce((sum, item) => sum + item.num, 0)
return total
}
},
computed: {
totalCount() {
console.log("computed被执行了");
let total = this.list.reduce((sum, item) => sum + item.num, 0)
return total
}
}
})
script>
body>
html>