倒计时代码

    function getRTime(){
        var EndTime= new Date('2015/01/13 10:00:00'); //截止时间
        var NowTime = new Date();
        var t =EndTime.getTime() - NowTime.getTime();

        var d=Math.floor(t/1000/60/60/24);
        var h=Math.floor(t/1000/60/60%24);
        var m=Math.floor(t/1000/60%60);
        var s=Math.floor(t/1000%60);

        document.getElementById("t_d").innerHTML = d + "天";
        document.getElementById("t_h").innerHTML = h + "时";
        document.getElementById("t_m").innerHTML = m + "分";
        document.getElementById("t_s").innerHTML = s + "秒";
    }
    setInterval(getRTime,1000);

<span id="t_d">00 天</span> <span id="t_h">00 时</span> <span id="t_m">00 分</span> <span id="t_s">00 秒</span>