最简单的JavaScript倒数计时器？

一尘不染

最简单的JavaScript倒数计时器？

javascript

只是想问问如何创建最简单的倒数计时器。

该网站上会有一句话：

“注册将在05:00分钟后关闭！”

因此，我想做的是创建一个简单的js倒数计时器，该计时器从“ 05:00”到“ 00:00”，然后在结束时重置为“ 05:00”。

之前我一直在回答一些问题，但是对于我想做的事情，它们似乎都太过激烈了（日期对象等）。

阅读 467

2020-04-25

共1个答案

一尘不染

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，并且都变得如此简单。

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>





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，其他所有startTimer功能均无法实现。

2020-04-25