我有两个演示，一个带演示，一个不带演示jQuery。两者都不使用日期函数，并且变得尽可能简单。
带有香草JavaScript的演示
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>
jQuery演示
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);
});
但是，如果您想要一个更精确的计时器，但只是稍微复杂一点：
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，我们已经做了一些非常简单的计时器，我们可以开始考虑可重用性和分离关注点了。为此，我们可以问“倒数计时器应该做什么？”
- 倒数计时器应该倒数吗？是
- 倒数计时器应该知道如何在DOM上显示自己吗？没有
- 倒数计时器在达到0时是否应该知道重新启动吗？没有
- 倒数计时器是否应该为客户提供剩余时间的方式？是
因此，请记住这些事情，让我们写出更好的（但仍然很简单） 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，为什么这种实现比其他实现更好呢？以下是一些您可以使用它的示例。请注意，除了第一个示例以外，所有其他startTimer功能都无法实现。
一个以XX：XX格式显示时间并在到达00:00后重新启动的示例
以两种不同格式显示时间的示例
一个示例，其中有两个不同的计时器，只有一个重新启动
按下按钮时启动倒数计时器的示例