JavaScript实现支付倒计时自动返回首页功能

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .wrapper{
            background-color:aquamarine;
            width: 300px;
            height: 300px;
            margin: 0 auto;
        }
        h2{
            text-align: center;
        }
        button{
            text-align: center; 
            margin-left: 68px;
        }
    </style>
</head>
<body>
    <div class="wrapper">
      <h2>商品:smile</h2>
      <h2>价格:infinity</h2>
      <h2>支付方式:Net</h2>
      <h2>订单号:123456789</h2>
      <button>取消</button>
      <button>支付</button>
    </div>
 
    <script>
        //逻辑:点击支付按钮进行跳转页面
        //获得第二个(第一个是0)标签名为'button'的标签添加点击事件并且绑定一个函数
        document.getElementsByTagName('button')[1].onclick = function(){
            //跳转前的确认框
            let res = window.confirm('请确认支付');
            //判断是否为真,为真跳转
            if(res){
                //直接使用目录下的html页面,也可输入其他网站链接
                location.href = "./return.html"
            }
        }
    </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .wrapper{
            width: 300px;
            height: 400px;
            margin: 0 auto;
        }
        .content{
            text-align: center;
        }
    </style>
</head>
<body>
    <div class="wrapper">
        <div class="content">
        <h2>支付成功</h2>
        <span id="countDown">10</span>秒后返回首页
        <button>立即返回</button>
        </div>
    </div>
 
    <script>
        //逻辑:页面打开,开始倒计时
        window.onload = function(){
            //先赋值
            let timer = 10;
            //倒计时
            //箭头函数()=>{} == function(){}
            setInterval(()=>{
                timer--;
                document.getElementById('countDown').innerText = timer;
                //等于0时跳转首页
                if(timer==0){
                    location.href = "./index.html"
                }
            },1000);
        }
        //点击按钮立即返回首页
        document.getElementsByTagName('button')[0].onclick = function(){
            location.href = "./index.html"
        }
    </script>
</body>
</html>