```
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<script src="https://cdn.bootcss.com/vue/2.5.18-beta.0/vue.js"></script>
</head>
<body>
<div id="app">
{{sum}}
</div>
<script>
new Vue({
el:"#app",
data:{
num1:10,
num2:20,
num3:30
},
computed:{
sum(){
return this.num1 + this.num2
}
},
// sum值发生改变触发
updated() {
console.log(this.sum)
},
})
</script>
</body>
</html>
```
