侦听器watch，实时更新属性
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>侦听器</title>
</head>
<body>
<div id="box">
用户名:<input type="text" v-model="username"> <br>
<h3>{{length}}</h3>
<h3 v-show="isShow" :style="warning">{{message}}</h3>
</div>
<script src="js/vue.js"></script>
<script>
new Vue({
el: '#box',
data: {
username: '',
length: 0,
message: '用户名过短',
isShow: false,
warning: 'color:red'
},
watch: {
username: function () {
this.length=this.username.length;
//console.log(this.username);
if (this.length < 6) {
this.isShow = true;
} else {
this.isShow = false;
}
}
}
});
</script>
</body>
</html>侦听器:实时监测页面中数据的变化
实时更新数据模型中的属性,并完成指定的动作
watch中侦听的属性必须是页面中的变量