Vue.js 监听属性 watch，我们可以通过 watch 来响应数据的变化。
以下实例通过使用 watch 实现计数器：
<body>
<div id = "app">
<p style = "font-size:25px;">计数器: {{ counter }}</p>
<button @click = "counter++" style = "font-size:25px;">点我</button>
</div>
<script type = "text/javascript">
var vm = new Vue({
el: '#app',
data: {
counter: 1
}
});
vm.$watch('counter', function(nval, oval) {
alert('计数器值的变化 :' + oval + ' 变为 ' + nval + '!');
});
</script>
-----------也可以改成-------------------
<div id = "app">
<p style = "font-size:25px;">计数器: {{ counter }}</p>
<!-- <button @click = "counter++" style = "font-size:25px;">点我</button>-->
<button @click = "countClick" style = "font-size:25px;">点我</button>
</div>
</body>
</html>
<script type = "text/javascript">
var vm = new Vue({
el: '#app',
data: {
counter: 1
},
methods:{
countClick: function(){
return this.counter ++;
}
}
});
vm.$watch('counter', function(nval, oval) {
alert('计数器值的变化 :' + oval + ' 变为 ' + nval + '!');
});
</script>