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);