js选中html的数字设置倒计时,JavaScript实现简单的数字倒计时

// 开始运行

function run() {

startB.disabled = true;

endB.disabled = false;

counter = 0;

// 初始化开始时间

startTime = new Date().valueOf();

// nextelapse是定时时间,初始时为100毫秒

// 注意setInterval函数: 时间逝去nextelapse(毫秒)后,onTimer才开始执行

timer = window.setInterval("onTimer()",nextelapse);

}

// 停止运行

function stop() {

startB.disabled = false;

endB.disabled = true;

window.clearTimeout(timer);

}

window.onload = function() {

endB.disabled = true;

};

// 倒计时函数

function onTimer()

{

if (start == finish)

{

window.clearInterval(timer);

alert("time is up!");

return;

}

var hms = new String(start).split(":");

var ms = new Number(hms[3]);

var s = new Number(hms[2]);

var m = new Number(hms[1]);

var h = new Number(hms[0]);

ms -= 10;

if (ms < 0)

{

ms = 90;

s -= 1;

if (s < 0)

{

s = 59;

m -= 1;

}

if (m < 0)

{

m = 59;

h -= 1;

}

}

var ms = ms < 10 ? ("0" + ms) : ms;

var ss = s < 10 ? ("0" + s) : s;

var sm = m < 10 ? ("0" + m) : m;

var sh = h < 10 ? ("0" + h) : h;

start = sh + ":" + sm + ":" + ss + ":" + ms;

clock.innerText = start;

// 清除上一次的定时器

window.clearInterval(timer);

// 自校验系统时间得到时间差,并由此得到下次所启动的新定时器的时间nextelapse

counter++;

var counterSecs = counter * 100;

var elapseSecs = new Date().valueOf() - startTime;

var diffSecs = counterSecs - elapseSecs;

nextelapse = normalelapse + diffSecs;

diff.value = counterSecs + "-" + elapseSecs + "=" + diffSecs;

next.value = "nextelapse = " + nextelapse;

if (nextelapse < 0) nextelapse = 0;

// 启动新的定时器

timer = window.setInterval("onTimer()",nextelapse);

}