Vue学习之vue中的计算属性和侦听器

<!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>vue</title>
    <script src="vue.js"></script>
</head>
<body>

    <!-- vue中的计算属性和侦听器
        计算属性：
        computed:{}
        性能高，当依赖的数据没有发生变化时，不会重新加载

        侦听器：
        watch
     -->

    <div id="root">
        姓：<input v-model="firstname" />
        名：<input v-model="lastname" />
        <div>{{fullName}}</div>
        <div>{{count}}</div>
    </div>

    <script>
        new Vue({
            el:"#root",
            data:{
                firstname:'',
                lastname:'',
                count: 0
            },
            computed:{
                fullName: function() {
                    return this.firstname + ' ' + this.lastname
                }
            },
            watch: {
              firstname: function() {
                  this.count ++
              },
              lastname: function() {
                  this.count ++
              },
              fullName: function() {
                  this.count ++
              }
             }
        })
    </script>
</body>
</html>