<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<div id="app">
    {{ a }}
</div>
<script src="vue.js"></script>
<script>
    //el  element 缩写 指定vue管理的试图，某个盒子的选择器
    //data vue中对象

    var data = {a: 1}

    const vm = new Vue({el: "#app", data: data});
    vm.$data.a = "5";
    vm.$watch('a', function (newVal, oldVal) {
            console.log(newVal, oldVal)
        });
    vm.$data.a = "6.................";

</script>
</body>

</html>

vue watch 监听数据变化_javascript