js倒计时（可定义截止日期）

<div id="times_wrap" class="time_num">
距离结束时间：
<div class="time_w">
<b id="times_d" class="time"> </b>天
<b id="times_h" class="time"> </b>时
<b id="times_m" class="time"> </b>分
<b id="times_s" class="time"> </b>秒
</div>
</div>

var time_wrap = document.getElementById("times_wrap");
var time_d = document.getElementById("times_d");
var time_h = document.getElementById("times_h");
var time_m = document.getElementById("times_m");
var time_s = document.getElementById("times_s");

var time_end = new Date("2015/9/30 18:00:00");  // 设定结束时间
time_end = time_end.getTime();

function show_time(){
var time_now = new Date();  // 获取当前时间
time_now = time_now.getTime();
var time_distance = time_end - time_now;  // 结束时间减去当前时间
var int_day, int_hour, int_minute, int_second;
if(time_distance >= 0){
// 天时分秒换算
int_day = Math.floor(time_distance/86400000)
time_distance -= int_day * 86400000;
int_hour = Math.floor(time_distance/3600000)
time_distance -= int_hour * 3600000;
int_minute = Math.floor(time_distance/60000)
time_distance -= int_minute * 60000;
int_second = Math.floor(time_distance/1000)

// 时分秒为单数时、前面加零站位
if(int_hour < 10)
int_hour = "0" + int_hour;
if(int_minute < 10)
int_minute = "0" + int_minute;
if(int_second < 10)
int_second = "0" + int_second;

// 显示时间
time_d.innerHTML = int_day;
time_h.innerHTML = int_hour;
time_m.innerHTML = int_minute;
time_s.innerHTML = int_second;
}else{
time_d.innerHTML = time_d.innerHTML;
time_h.innerHTML = time_h.innerHTML;
time_m.innerHTML = time_m.innerHTML;
time_s.innerHTML = time_s.innerHTML;
}
};
window.setInterval(function(){
show_time();
}, 1000);