我想使用一个简单的倒数计时器，从运行函数开始30秒开始，到0结束。没有毫秒。怎么编码？
答案 0 :(得分：249)
var count=30;
var counter=setInterval(timer, 1000); //1000 will run it every 1 second
function timer()
{
count=count-1;
if (count <= 0)
{
clearInterval(counter);
//counter ended, do something here
return;
}
//Do code for showing the number of seconds here
}
要使计时器的代码出现在段落中（或页面上的任何其他位置），只需输入以下行：
<span id="timer"></span>
您希望秒出现的位置。然后在timer()函数中插入以下行，如下所示：
function timer()
{
count=count-1;
if (count <= 0)
{
clearInterval(counter);
return;
}
document.getElementById("timer").innerHTML=count + " secs"; // watch for spelling
}
答案 1 :(得分：100)
我前段时间写过这个剧本：
用法：
var myCounter = new Countdown({
seconds:5, // number of seconds to count down
onUpdateStatus: function(sec){console.log(sec);}, // callback for each second
onCounterEnd: function(){ alert('counter ended!');} // final action
});
myCounter.start();
function Countdown(options) {
var timer,
instance = this,
seconds = options.seconds || 10,
updateStatus = options.onUpdateStatus || function () {},
counterEnd = options.onCounterEnd || function () {};
function decrementCounter() {
updateStatus(seconds);
if (seconds === 0) {
counterEnd();
instance.stop();
}
seconds--;
}
this.start = function () {
clearInterval(timer);
timer = 0;
seconds = options.seconds;
timer = setInterval(decrementCounter, 1000);
};
this.stop = function () {
clearInterval(timer);
};
}
答案 2 :(得分：53)
到目前为止，答案似乎依赖于即时运行的代码。如果您将计时器设置为1000毫秒，则实际上将大约为1008。
您应该如何做到这一点：
function timer(time,update,complete) {
var start = new Date().getTime();
var interval = setInterval(function() {
var now = time-(new Date().getTime()-start);
if( now <= 0) {
clearInterval(interval);
complete();
}
else update(Math.floor(now/1000));
},100); // the smaller this number, the more accurate the timer will be
}
要使用，请致电：
timer(
5000, // milliseconds
function(timeleft) { // called every step to update the visible countdown
document.getElementById('timer').innerHTML = timeleft+" second(s)";
},
function() { // what to do after
alert("Timer complete!");
}
);
答案 3 :(得分：21)
如果有人需要分钟和秒钟，那么这是另一个：
var mins = 10; //Set the number of minutes you need
var secs = mins * 60;
var currentSeconds = 0;
var currentMinutes = 0;
/*
* The following line has been commented out due to a suggestion left in the comments. The line below it has not been tested.
* setTimeout('Decrement()',1000);
*/
setTimeout(Decrement,1000);
function Decrement() {
currentMinutes = Math.floor(secs / 60);
currentSeconds = secs % 60;
if(currentSeconds <= 9) currentSeconds = "0" + currentSeconds;
secs--;
document.getElementById("timerText").innerHTML = currentMinutes + ":" + currentSeconds; //Set the element id you need the time put into.
if(secs !== -1) setTimeout('Decrement()',1000);
}
答案 4 :(得分：3)
// Javascript Countdown
// Version 1.01 6/7/07 (1/20/2000)
// by TDavid at http://www.tdscripts.com/
var now = new Date();
var theevent = new Date("Sep 29 2007 00:00:01");
var seconds = (theevent - now) / 1000;
var minutes = seconds / 60;
var hours = minutes / 60;
var days = hours / 24;
ID = window.setTimeout("update();", 1000);
function update() {
now = new Date();
seconds = (theevent - now) / 1000;
seconds = Math.round(seconds);
minutes = seconds / 60;
minutes = Math.round(minutes);
hours = minutes / 60;
hours = Math.round(hours);
days = hours / 24;
days = Math.round(days);
document.form1.days.value = days;
document.form1.hours.value = hours;
document.form1.minutes.value = minutes;
document.form1.seconds.value = seconds;
ID = window.setTimeout("update();", 1000);
}<p><font face="Arial" size="3">Countdown To January 31, 2000, at 12:00: </font>
</p>
<form name="form1">
<p>Days
<input type="text" name="days" value="0" size="3">Hours
<input type="text" name="hours" value="0" size="4">Minutes
<input type="text" name="minutes" value="0" size="7">Seconds
<input type="text" name="seconds" value="0" size="7">
</p>
</form>
答案 5 :(得分：1)
根据接受的答案进行扩展，您的机器进入睡眠状态等可能会延迟计时器的工作。你可以花一点时间来获得真正的时间。这将留下真正的时间。
<span id="timer"></span>
<script>
var now = new Date();
var timeup = now.setSeconds(now.getSeconds() + 30);
//var timeup = now.setHours(now.getHours() + 1);
var counter = setInterval(timer, 1000);
function timer() {
now = new Date();
count = Math.round((timeup - now)/1000);
if (now > timeup) {
window.location = "/logout"; //or somethin'
clearInterval(counter);
return;
}
var seconds = Math.floor((count%60));
var minutes = Math.floor((count/60) % 60);
document.getElementById("timer").innerHTML = minutes + ":" + seconds;
}
</script>
答案 6 :(得分：1)
刚刚修改过@ClickUpvote's answer：
您可以使用IIFE (Immediately Invoked Function Expression)和递归使它更容易一些：
var i = 5; //set the countdown
(function timer(){
if (--i < 0) return;
setTimeout(function(){
console.log(i + ' secs'); //do stuff here
timer();
}, 1000);
})();
var i = 5;
(function timer(){
if (--i < 0) return;
setTimeout(function(){
document.getElementsByTagName('h1')[0].innerHTML = i + ' secs';
timer();
}, 1000);
})();<h1>5 secs</h1>
答案 7 :(得分：0)
您可以使用纯JS执行以下操作。你只需要提供具有秒数的函数，它将完成剩下的工作。
var insertZero = n => n < 10 ? "0"+n : ""+n,
displayTime = n => n ? time.textContent = insertZero(~~(n/3600)%3600) + ":" +
insertZero(~~(n/60)%60) + ":" +
insertZero(n%60)
: time.textContent = "IGNITION..!",
countDownFrom = n => (displayTime(n), setTimeout(_ => n ? sid = countDownFrom(--n)
: displayTime(n), 1000)),
sid;
countDownFrom(3610);
setTimeout(_ => clearTimeout(sid),20005);<div id="time"></div>
答案 8 :(得分：0)
基于@Layton Everson提出的解决方案，我开发了一个包括小时，分钟和秒的计数器：
var initialSecs = 86400;
var currentSecs = initialSecs;
setTimeout(decrement,1000);
function decrement() {
var displayedSecs = currentSecs % 60;
var displayedMin = Math.floor(currentSecs / 60) % 60;
var displayedHrs = Math.floor(currentSecs / 60 /60);
if(displayedMin <= 9) displayedMin = "0" + displayedMin;
if(displayedSecs <= 9) displayedSecs = "0" + displayedSecs;
currentSecs--;
document.getElementById("timerText").innerHTML = displayedHrs + ":" + displayedMin + ":" + displayedSecs;
if(currentSecs !== -1) setTimeout(decrement,1000);
}
答案 9 :(得分：0)
// Javascript Countdown
// Version 1.01 6/7/07 (1/20/2000)
// by TDavid at http://www.tdscripts.com/
var now = new Date();
var theevent = new Date("Nov 13 2017 22:05:01");
var seconds = (theevent - now) / 1000;
var minutes = seconds / 60;
var hours = minutes / 60;
var days = hours / 24;
ID = window.setTimeout("update();", 1000);
function update() {
now = new Date();
seconds = (theevent - now) / 1000;
seconds = Math.round(seconds);
minutes = seconds / 60;
minutes = Math.round(minutes);
hours = minutes / 60;
hours = Math.round(hours);
days = hours / 24;
days = Math.round(days);
document.form1.days.value = days;
document.form1.hours.value = hours;
document.form1.minutes.value = minutes;
document.form1.seconds.value = seconds;
ID = window.setTimeout("update();", 1000);
}<p><font face="Arial" size="3">Countdown To January 31, 2000, at 12:00: </font>
</p>
<form name="form1">
<p>Days
<input type="text" name="days" value="0" size="3">Hours
<input type="text" name="hours" value="0" size="4">Minutes
<input type="text" name="minutes" value="0" size="7">Seconds
<input type="text" name="seconds" value="0" size="7">
</p>
</form>
答案 10 :(得分：0)
我的解决方案适用于MySQL日期时间格式并提供回调函数。在complition。 免责声明：仅适用于分钟和秒钟，因为这是我需要的。
jQuery.fn.countDownTimer = function(futureDate, callback){
if(!futureDate){
throw 'Invalid date!';
}
var currentTs = +new Date();
var futureDateTs = +new Date(futureDate);
if(futureDateTs <= currentTs){
throw 'Invalid date!';
}
var diff = Math.round((futureDateTs - currentTs) / 1000);
var that = this;
(function countdownLoop(){
// Get hours/minutes from timestamp
var m = Math.floor(diff % 3600 / 60);
var s = Math.floor(diff % 3600 % 60);
var text = zeroPad(m, 2) + ':' + zeroPad(s, 2);
$(that).text(text);
if(diff <= 0){
typeof callback === 'function' ? callback.call(that) : void(0);
return;
}
diff--;
setTimeout(countdownLoop, 1000);
})();
function zeroPad(num, places) {
var zero = places - num.toString().length + 1;
return Array(+(zero > 0 && zero)).join("0") + num;
}
}
// $('.heading').countDownTimer('2018-04-02 16:00:59', function(){ // on complete})
答案 11 :(得分：0)
出于性能考虑，我们现在可以安全地使用requestAnimationFrame进行快速循环，而不用使用setInterval / setTimeout。
使用setInterval / setTimeout时，如果循环任务花费的时间比间隔时间长，浏览器将简单地延长间隔循环，以继续完整渲染。这正在制造问题。在 setInterval / setTimeout超载几分钟后，这可以冻结选项卡，浏览器或整个计算机。
Internet设备具有广泛的性能，因此，很难对固定的间隔时间（以毫秒为单位）进行硬编码！
使用Date object比较开始日期和当前日期。这比其他方法快得多，浏览器将以稳定的 60FPS （1000/60 = 16.66ms by frame ）- {{ 3}} -，如果循环中的任务要求更多，浏览器将删除一些重绘。
这可以让我们留出余地（人类= 24FPS => 1000/24 = 41.66ms，每帧=流畅的动画！）
/* Seconds to (STRING)HH:MM:SS.MS ------------------------*/
/* This time format is compatible with FFMPEG ------------*/
function secToTimer(sec){
const o = new Date(0), p = new Date(sec * 1000)
return new Date(p.getTime()-o.getTime()).toString().split(" ")[4] + "." + p.getMilliseconds()
}
/* Countdown loop ----------------------------------------*/
let job, origin = new Date().getTime()
const timer = () => {
job = requestAnimationFrame(timer)
OUT.textContent = secToTimer((new Date().getTime() - origin) / 1000)
}
/* Start looping -----------------------------------------*/
requestAnimationFrame(timer)
/* Stop looping ------------------------------------------*/
// cancelAnimationFrame(job)
/* Reset the start date ----------------------------------*/
// origin = new Date().getTime()span {font-size:4rem}<span id="OUT"></span>
<br>
<button onclick="origin = new Date().getTime()">RESET</button>
<button onclick="requestAnimationFrame(timer)">RESTART</button>
<button onclick="cancelAnimationFrame(job)">STOP</button>