js简单倒计时实现代码

<div class="time">

 距离活动结束还有<span id="day"></span>天

 <span id="hours"></span>小时

 <span id="min"></span>分

 <span id="sec"></span>秒

</div>

<script type="text/javascript">

var day = document.getElementById("day");

var hours = document.getElementById("hours");

var min = document.getElementById("min");

var sec = document.getElementById("sec");

var DifferenceHour = -1;

var DifferenceMinute = -1;

var DifferenceSecond = -1;

//var Tday = new Date("07 20,2016 10:00:00")  //**倒计时时间点-注意格式

var Tday = new Date("07/20/2016 10:00:00");  //IE:月/日/年

var daysms = 24 * 60 * 60 * 1000;

var hoursms = 60 * 60 * 1000;

var Secondms = 60 * 1000;

var microsecond = 1000;

function clock () {

 var time = new Date();

 var hour = time.getHours();

 var minute = time.getMinutes();

 var second = time.getSeconds();

 var timevalue = "" + ((hour > 12) ? hour-12:hour);

 timevalue += ((minute < 10) ? ":0":":") + minute;

 timevalue += ((second < 10) ? ":0":":") + second;

 timevalue += ((hour > 12) ? " PM":" AM");

 // document.formnow.now.value = timevalue

 var convertHour = DifferenceHour;

 var convertMinute = DifferenceMinute;

 var convertSecond = DifferenceSecond;

 var Diffms = Tday.getTime() - time.getTime();

 DifferenceHour = Math.floor(Diffms / daysms);

 Diffms -= DifferenceHour * daysms;

 DifferenceMinute = Math.floor(Diffms / hoursms);

 Diffms -= DifferenceMinute * hoursms;

 DifferenceSecond = Math.floor(Diffms / Secondms);

 Diffms -= DifferenceSecond * Secondms;

 var dSecs = Math.floor(Diffms / microsecond);

 if (convertHour != DifferenceHour) {

 day.innerHTML = DifferenceHour;

 }

 if (convertMinute != DifferenceMinute) {

 hours.innerHTML = DifferenceMinute;

 }

 if (convertSecond != DifferenceSecond) {

 min.innerHTML = DifferenceSecond;

 }

 sec.innerHTML = dSecs;

 // document.formnow.Tnow.value= DifferenceHour DifferenceMinute + DifferenceSecond + dSecs

 setTimeout("clock()", 1000);

}

clock();

</script>