<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<div id="app">
<p>{{num}}</p>
<button @click="changeAdd">changeAdd</button>
<button @click="changeReduce">changeReduce</button>
</div>
<script src="https://cdn.bootcss.com/vue/2.6.11/vue.js"></script>
<script>
// watch侦听检测数据 一般用于检测属性
new Vue({
el:"#app",
data(){
return {
num:0
}
},
methods:{
changeAdd(){
this.num++
},
changeReduce(){
this.num--
}
},
watch:{
num(newNUm,oldNum){
console.log(newNUm,oldNum);
if (newNUm<0){
this.num=0
}
}
}
})
</script>
</body>
</html>
Python3Turtle