效果：
javascript：
<script type="text/javascript">
function countTime() {
//获取当前时间
var date = new Date();
var now = date.getTime();
//设置截止时间
var endDate = new Date("2018-10-25 00:00:00");
var end = endDate.getTime();
//时间差
var differTime = end - now;
//定义变量,h,m,s保存倒计时的时间
var h, m, s;
if (differTime >= 0) {
h = Math.floor(differTime / 1000 / 60 / 60);
m = Math.floor(differTime / 1000 / 60 % 60);
s = Math.floor(differTime / 1000 % 60);
h = h < 10 ? ("0" + h) : h;
m = m < 10 ? ("0" + m) : m;
s = s < 10 ? ("0" + s) : s;
document.getElementById("_h").innerHTML = h + "时";
document.getElementById("_m").innerHTML = m + "分";
document.getElementById("_s").innerHTML = s + "秒";
setTimeout(countTime, 1000);
} else {
document.getElementById("_h").innerHTML = "00时";
document.getElementById("_m").innerHTML = "00分";
document.getElementById("_s").innerHTML = "00秒";
}
}
</script>
HTML:
<body onload="countTime()">
<div class="timer">
<span id="_h"></span>
<span id="_m"></span>
<span id="_s"></span>
</div>
</body>