js倒计时功能

<input id="countdown" type="text" value="140时50分20秒">

<script>
var oCountdown = document.getElementById("countdown"),
    nowStamps = Date.now() - 100,            // 服务器当前时间
    endStamps = Date.now() + 50000 - 100,    // 活动结束时间戳
    diff = nowStamps - Date.now();            // 本地时间和服务器时间差

function updateCountdown(nowStamps) {
    var timeLeft = (endStamps - nowStamps)/1000,
        hour = parseInt(timeLeft/3600),
        minute = parseInt(timeLeft%3600/60),
        seconds = parseInt(timeLeft%60);

    oCountdown.value = hour + "时" + minute + "分" + seconds + "秒";

    return timeLeft;
}

function run() {
    nowStamps = Date.now() + diff;    // 服务器当前时间
    if (updateCountdown(nowStamps) > 0) {    // 更新倒计时时间
        setTimeout(run, 100);    // fix + 100 调整误差
    } else {
        oCountdown.value = "活动已结束";
    }
}
setTimeout(run, 100);
</script>