在做计时器案例时出现了 Cannot set properties of null(setting ‘innerHTML‘)-优快云博客

本文链接：https://blog.youkuaiyun.com/mastercao/article/details/123513826

查找了一会别的博主说是因为计时器放置的位置不对应该在body最下边放置结果照做之后还是报错。

然后我意识到了在获取元素时元素的类名前没有加点真的是粗心大意了这也提醒了我们在注册事件时类名前一定要加点。哈哈哈哈哈哈~

<!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>
        span{
            /* position: absolute; */
            float: left;
            width: 40px;
            height: 40px;
            background-color: black;
            color: #999;    
            border: 1px solid white;
            

        }
        .clearfix::after,
        .clearfix::before {
            content: '';
            display: block;
            clear: both;
        }
    </style>
</head>
<body>
    <div>
        <span class="hour">1</span>
        <span class="minute">2</span>
        <span class="second">3</span>
    </div>
    <script>
        var hour = document.querySelector('.hour');
        var minute = document.querySelector('.minute');
        var second = document.querySelector('.second');
        var inputTime = +new Date('2022-3-15 22:00:00');
        setInterval(countDown,1000);
        function countDown() {
            var nowTime = +new Date();  //  返回一个当前时间的总毫秒数
            var times = (inputTime - nowTime) / 1000;  // times是剩余时间总的毫秒

            var h = parseInt(times / 60 / 60 % 24); // 计算小时
            h = h < 10 ? '0' + h : h;
            hour.innerHTML = h;
            var m = parseInt(times / 60 % 60);     // 计算分数
            m = m < 10 ? '0' + m : m;
            minute.innerHTML = m;
            var s = parseInt(times % 60);        // 计算当前秒数
            s = s < 10 ? '0' + s : s;
            second.innerHTML = s;
        }
        
        
    </script>
</body>    
</html>