JavaScript 实现前端下班倒计时显示功能

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>js倒计时显示-细数逝去的过往</title>
<style type="text/css">
#clock {
font: bold 24pt sans;
background-color: #f5f5f5;
padding: 10px 15px;
border: 1px solid #ccc;
border-radius: 5px;
}
.demo {
position: absolute;
margin-left: 40%;
margin-top: 40%;
}
</style>
</head>
<body>
<div class="demo">
<center>
<h1>下班倒计时显示</h1>
</center>
<span id="clock"></span>
</div>
<script>
function displayTime() {
var elt = document.getElementById("clock");
if(leftTime < 0) {
elt.innerHTML = "Over";
} else {
var endTime = new Date("2016/11/21 18:00:00");
var now = new Date();
var leftTime = endTime.getTime() - now.getTime();
var ms = parseInt(leftTime % 1000).toString();
leftTime = parseInt(leftTime / 1000);
var o = Math.floor(leftTime / 3600);
var d = Math.floor(o / 24);
var m = Math.floor(leftTime / 60 % 60);
var s = leftTime % 60;
elt.innerHTML = o + "小时:" + m + "分:" + s + "秒:" + ms.charAt(0);
setTimeout(displayTime, 100);
}
}
displayTime();
</script>
</body>
</html>