Can't the value of the object property modified by Vue.set be updated at the interpolation?

<!--
* @Author: chj
* @FileName:vue.set.html
* @Date:   2018-06-22 13:58:18
* @Last Modified by:   chj
* @Last Modified time: 2018-06-22 16:10:47
-->
<!DOCTYPE html>
<html lang="cmn-hans">

<head>
    <meta charset="utf-8">
    <meta http-equiv=X-UA-Compatible content="IE=edge,chrome=1">
    <meta name="renderer" content="webkit">
    <script src="../assets/js/vue.js" type="text/javascript"></script>
    <title>vue.set</title>
</head>
<body>
    <h1>vue.set</h1>
    <hr>
    <div id="app">
        <ol>
            <li>:{{outData.Name}}</li>
            <li>:{{outData.Age}}</li>
            <li>:{{outData.School}}</li>
            <li v-show="isShow">:{{outData.class}}</li>
            <li v-if="isTrue">:{{outData.No}}</li>
        </ol>
        <button @click="plus" id="btn1"></button>
        <button onclick="changeClass()" id="btn2"></button>
        <ol>
            <ul>
                <li v-for=" value in arr">{{value}}</li>
            </ul>
        </ol>
        <button onclick="add()"></button>
    </div>
    <script type="text/javascript">
    //
    var outData = {
        Name: "",
        Age: 18,
        School: ""
    }

     //
    function changeClass() {
        Vue.set(outData, "class", "10");
        console.log("outData.class:"+outData.class);
    }

    function add() {
        //app.arr[1] = "ddd";
        Vue.set(app.arr,1,"ddd");
        console.log(app.arr[1]);
    }
    var app = new Vue({
        el: "-sharpapp",
        data: {
            outData: outData,
            isTrue: false,
            isShow: false,
            class: "5",
            arr: ["aaa", "bbb", "ccc"]
        },
        methods: {
            plus: function() {
                this.isTrue = true;
                this.isShow = true;
                outData["No"] = "123";
                outData["class"] = this.class;
                console.log("outData.class:"+outData.class);
            },
        }
    })
    </script>
</body>

</html>

when you click btn1 and btn2, the values are 5 and 10.

, respectively.

but the value in the page is still 5. Why is this

?
Mar.21,2021

this.outData.class = this.class


Vue.set (app.outData, "class", "10")

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b3887b-2c125.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3887b-2c125.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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