一个简单的倒计时
在界面会显示数字倒数，等到数字为0时，弹出提示框
<body>
<div class="box">
<span class="clock">60</span>
</div>
<script src="https://cdn.bootcss.com/jquery/3.4.1/jquery.js"></script>
<script type="text/javascript">
let time;
window.onload = function countDown() {
let time_num = 60;
time = setInterval(function () {
time_num--;
$(".clock").html(time_num);
if (time_num == -1) {
clearInterval(time);
alert("倒计时结束");
$(".clock").html(0);
}
}, 100);
};
</script>
</body>
