// 倒计时
var fnTimeCountDown = function (time) {
    var time = new Date(time).getTime() - new Date().getTime(), // 倒计时时间转变为毫秒数
        days, hours, min, sec, temp;

    if (time <= 0) {
        return null;
    }

    days = Math.floor(time / (24*3600*1000));

    temp = time % (24*3600*1000); // 不够天的转换成小时
    hours = Math.floor(temp / (3600*1000));

    temp = temp % (3600*1000);  // 剩余的分钟数
    min = Math.floor(temp / (60*1000));

    temp = temp % (60*1000);
    sec = Math.floor(temp / (1000));

    // 格式化："05"
    var zero = function (n) {
        var n = parseInt(n, 10);
        if (n > 0) {
            if (n <= 9) {
                n = "0" + n;
            }
            return n;
        } else {
            return "00";
        }
    };

    return {
        days: days,
        hours: zero(hours),
        min: zero(min),
        sec: zero(sec)
    };
};

var future = "2014/01/01 00:00",
    countobj = null,
    timer = null,
    countdown = function (time, callback) {
        // 倒计时数据对象：countobj
        countobj = fnTimeCountDown(time);
        callback && callback(countobj);

        if (countobj) {
            timer = setTimeout(function () {
                countdown(time, callback);
            }, 1000);
        } else {
            // 倒计时结束
            clearTimeout(timer);
        }
    };

setTimeout(function () {
    countdown(future, function (obj) {
   
        if (obj) {
            // 倒计时应用
            console.log(obj);
        } else {
            // 倒计时结束
            console.log("countdown over!");
        }
    });
}, 0);

javascript 倒计时