倒计时

function countDown (dateStr) {
    var end = +new Date(dateStr),
        start = +new Date(),
        during = Math.floor((end - start)/1000);
    var day = Math.floor( during/(24*60*60) ),
        t1 = during - (day*24*60*60),
        hour = Math.floor( t1/(60*60) ),
        t2 = t1 - hour*60*60,
        min = Math.floor( t2/60 ),
        sec = t2%60;

    return day + '天' + hour + '小时' + min + '分' + sec + '秒';
}

setInterval(function(){
    var str = countDown('2016-01-01');
    document.write(str);
}, 1000);