如何在JavaScript写一个倒计时计时器?

小开

您可以使用setInterval轻松地创建计时器功能。下面是你可以用来创建计时器的代码。

window.onload = function() {
var minute = 5;
var sec = 60;
setInterval(function() {
document.getElementById("timer").innerHTML = minute + " : " + sec;
sec--;
if (sec == 00) {
minute --;
sec = 60;
if (minute == 0) {
minute = 5;
}
}
}, 1000);
}

Registration closes in <span id="timer">05:00<span> minutes!

小开

最佳答案

我有两个演示，一个与jQuery和一个没有。两者都不使用日期函数，而且都非常简单。

Demo with vanilla JavaScript

function startTimer(duration, display) {
var timer = duration, minutes, seconds;
setInterval(function () {
minutes = parseInt(timer / 60, 10);
seconds = parseInt(timer % 60, 10);


minutes = minutes < 10 ? "0" + minutes : minutes;
seconds = seconds < 10 ? "0" + seconds : seconds;


display.textContent = minutes + ":" + seconds;


if (--timer < 0) {
timer = duration;
}
}, 1000);
}


window.onload = function () {
var fiveMinutes = 60 * 5,
display = document.querySelector('#time');
startTimer(fiveMinutes, display);
};

<body>
<div>Registration closes in <span id="time">05:00</span> minutes!</div>
</body>

演示与jQuery

function startTimer(duration, display) {
var timer = duration, minutes, seconds;
setInterval(function () {
minutes = parseInt(timer / 60, 10);
seconds = parseInt(timer % 60, 10);


minutes = minutes < 10 ? "0" + minutes : minutes;
seconds = seconds < 10 ? "0" + seconds : seconds;


display.text(minutes + ":" + seconds);


if (--timer < 0) {
timer = duration;
}
}, 1000);
}


jQuery(function ($) {
var fiveMinutes = 60 * 5,
display = $('#time');
startTimer(fiveMinutes, display);
});

然而，如果你想要一个更精确的计时器，只是稍微复杂一点:

function startTimer(duration, display) {
var start = Date.now(),
diff,
minutes,
seconds;
function timer() {
// get the number of seconds that have elapsed since
// startTimer() was called
diff = duration - (((Date.now() - start) / 1000) | 0);


// does the same job as parseInt truncates the float
minutes = (diff / 60) | 0;
seconds = (diff % 60) | 0;


minutes = minutes < 10 ? "0" + minutes : minutes;
seconds = seconds < 10 ? "0" + seconds : seconds;


display.textContent = minutes + ":" + seconds;


if (diff <= 0) {
// add one second so that the count down starts at the full duration
// example 05:00 not 04:59
start = Date.now() + 1000;
}
};
// we don't want to wait a full second before the timer starts
timer();
setInterval(timer, 1000);
}


window.onload = function () {
var fiveMinutes = 60 * 5,
display = document.querySelector('#time');
startTimer(fiveMinutes, display);
};

<body>
<div>Registration closes in <span id="time"></span> minutes!</div>
</body>

现在我们已经制作了几个非常简单的计时器，我们可以开始考虑重用性和分离关注点了。我们可以通过问“倒计时计时器应该做什么?”来做到这一点。

倒计时计时器应该开始倒计时吗?是的
倒计时计时器应该知道如何在DOM上显示自己吗?没有
倒数计时器应该知道当它达到0时重新启动自己吗?没有
倒计时计时器是否应该为客户端提供一种访问剩余时间的方法?是的

因此，考虑到这些内容，让我们编写一个更好的(但仍然非常简单)CountDownTimer

function CountDownTimer(duration, granularity) {
this.duration = duration;
this.granularity = granularity || 1000;
this.tickFtns = [];
this.running = false;
}


CountDownTimer.prototype.start = function() {
if (this.running) {
return;
}
this.running = true;
var start = Date.now(),
that = this,
diff, obj;


(function timer() {
diff = that.duration - (((Date.now() - start) / 1000) | 0);


if (diff > 0) {
setTimeout(timer, that.granularity);
} else {
diff = 0;
that.running = false;
}


obj = CountDownTimer.parse(diff);
that.tickFtns.forEach(function(ftn) {
ftn.call(this, obj.minutes, obj.seconds);
}, that);
}());
};


CountDownTimer.prototype.onTick = function(ftn) {
if (typeof ftn === 'function') {
this.tickFtns.push(ftn);
}
return this;
};


CountDownTimer.prototype.expired = function() {
return !this.running;
};


CountDownTimer.parse = function(seconds) {
return {
'minutes': (seconds / 60) | 0,
'seconds': (seconds % 60) | 0
};
};

那么，为什么这个实现比其他实现更好呢?这里有一些你可以使用它的例子。注意，startTimer函数不能实现除第一个示例以外的所有示例。

以XX:XX格式显示时间，到达00:00后重启。

以两种不同格式显示时间的示例

一个例子，有两个不同的定时器，只有一个重启

当按下按钮时启动倒计时计时器的示例

小开

如果你想要一个真正的计时器，你需要使用date对象。

计算差值。

格式化字符串。

window.onload=function(){
var start=Date.now(),r=document.getElementById('r');
(function f(){
var diff=Date.now()-start,ns=(((3e5-diff)/1e3)>>0),m=(ns/60)>>0,s=ns-m*60;
r.textContent="Registration closes in "+m+':'+((''+s).length>1?'':'0')+s;
if(diff>3e5){
start=Date.now()
}
setTimeout(f,1e3);
})();
}

例子

< a href = " http://jsfiddle.net/HWGE2/4/ " > Jsfiddle < / >

计时器不那么精确

var time=5*60,r=document.getElementById('r'),tmp=time;


setInterval(function(){
var c=tmp--,m=(c/60)>>0,s=(c-m*60)+'';
r.textContent='Registration closes in '+m+':'+(s.length>1?'':'0')+s
tmp!=0||(tmp=time);
},1000);

如何在JavaScript写一个倒计时计时器?

< a href = " http://jsfiddle.net/HWGE2/4/ " > Jsfiddle < / >

< a href = " http://jsfiddle.net/HWGE2/5/ " > JsFiddle < / >