Question

只是想问一下如何创建最简单的倒数计时器。

网站上会有一句话：

“注册于05:00关闭！”

所以，我想要做的是创建一个简单的js倒计时器，从“05:00”到“00:00”，然后一旦结束就重置为“05:00”。

我以前经历过一些答案，但是对于我想做的事情，它们看起来都太强烈了（日期对象等）。

Answer 1

我有两个演示，一个有jQuery而另一个没有。既没有使用日期功能，也没有使用日期功能。

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>

Demo with 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);
});

但是，如果您想要一个更复杂的更准确的计时器：

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问题。我们可以通过询问“倒数计时器应该做什么来做到这一点”来做到这一点。

倒数计时器倒计时？是
倒计时器是否应该知道如何在DOM上显示自己？否
倒数计时器是否知道在达到0时自动重启？否
倒计时器是否应该为客户提供一种方式来访问剩余时间？的是

因此，考虑到这些事情，我们可以写一个更好的（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
  };
};

那么为什么这种实施比其他实施更好？以下是您可以使用它做些什么的一些示例。请注意，startTimer函数无法实现除第一个示例之外的所有示例。

An example that displays the time in XX:XX format and restarts after reaching 00:00

An example that displays the time in two different formats

An example that has two different timers and only one restarts

An example that starts the count down timer when a button is pressed

Answer 2

如果你想要一个真正的计时器，你需要使用日期对象。

计算差异。

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);
      })();
}

示例

Jsfiddle

不是那么精确的计时器

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);

JsFiddle

Answer 3

您可以使用setInterval轻松创建计时器功能.Below是您可以用它来创建计时器的代码。

http://jsfiddle.net/ayyadurai/GXzhZ/1/

window.onload = function() {
  var hour = 2;
  var sec = 60;
  setInterval(function() {
    document.getElementById("timer").innerHTML = hour + " : " + sec;
    sec--;
    if (sec == 00) {
      hour--;
      sec = 60;
      if (hour == 0) {
        hour = 2;
      }
    }
  }, 1000);
}

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

最简单的JavaScript倒计时器？

3 个答案:

Jsfiddle

JsFiddle