按钮改变和控制div的形状的html，JavaScript代码

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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
 <h1>JavaScript：验证输入JavaScript 常用于验证用户的输入</h1>
    <p>请输入数字。如果输入值不是数字，浏览器会弹出提示框。</p>
   <input type="text" id="demo01">
   <button  type="button " onclick="my()">提交验证</button>
   <script>
function my(){
    let yz =document.getElementById("demo01").value;
    if(yz==""||isNaN(yz)){
        alert("不是数字");

    }
    else{
        alert("欢迎光临");
    }

}

    </script>

</body>
</html>