【问题标题】：Countdown reset on specific time在特定时间倒计时重置
【发布时间】：2015-05-11 00:34:11
【问题描述】：

目前我有一个脚本，它有一个特定日期的倒计时，但我希望倒计时在计时器上是特定的，所以假设我启动计时器并且我已将计时器设置为运行 30 天，然后它将运行 30 天，然后再次重置为 30 天并开始运行。是否可以更改它来这样做？

我的代码：

    <body>

    <span id="countdown"></span>

    <script LANGUAGE="Javascript">

    // set the date we're counting down to
    var target_date = new Date("Apr 9, 2015").getTime();

    // variables for time units
    var days, hours, minutes, seconds;

    // get tag element
    var countdown = document.getElementById("countdown");

    // update the tag with id "countdown" every 1 second
    setInterval(function () {

        // find the amount of "seconds" between now and target
        var current_date = new Date().getTime();
        var seconds_left = (target_date - current_date) / 1000;

        // do some time calculations
        days = parseInt(seconds_left / 86400);
        seconds_left = seconds_left % 86400;

        hours = parseInt(seconds_left / 3600);
        seconds_left = seconds_left % 3600;

        minutes = parseInt(seconds_left / 60);
        seconds = parseInt(seconds_left % 60);

        // format countdown string + set tag value
        countdown.innerHTML = days + "d, " + hours + "h, "
        + minutes + "m, " + seconds + "s";  

    }, 1000);

</script>

</body>

编辑：

我现在已将代码更改为如下所示，但是现在当我在浏览器中打开网站时，它是空白的。

新代码：

<span id="countdown"></span>

<script LANGUAGE="Javascript">

// set the date we're counting down to
var target_date = new Date("Apr 9, 2015").getTime();

// variables for time units
var days, hours, minutes, seconds;

// get tag element
var countdown = document.getElementById("countdown");


if (seconds_left <= 0){
        target_date = target_date + 30 days;
    }


// update the tag with id "countdown" every 1 second
setInterval(function () {

// find the amount of "seconds" between now and target
var current_date = new Date().getTime();
var seconds_left = (target_date - current_date) / 1000;

// do some time calculations
days = parseInt(seconds_left / 86400);
seconds_left = seconds_left % 86400;

hours = parseInt(seconds_left / 3600);
seconds_left = seconds_left % 3600;

minutes = parseInt(seconds_left / 60);
seconds = parseInt(seconds_left % 60);

// format countdown string + set tag value
countdown.innerHTML = days + "d, " + hours + "h, "
+ minutes + "m, " + seconds + "s";  

}, 1000);

【问题讨论】：

当seconds_left <= 0 重新计算target_date target_date + 30 天。
您真的想在浏览器中安装这么大的计时器吗？无论如何，您始终可以在到达时间时使用clearInterval()清除间隔并重新开始。
我现在已经添加了这一行if (seconds_left <= 0){ target_date = target_date + 30 days; } 但是现在我的页面上什么都不会显示，它只是空白，在它显示倒计时之前在哪里？

标签： javascript html timer reset countdown

【解决方案1】：

我真的建议您利用 JavaScript 库，在您的情况下，moment JS 是完美的解决方案，您可以查看他们的文档并了解如何轻松管理时间。无论如何，这里是使用时刻 js 解决您问题的方法。

首先下载 moment js 并将其添加到您的页面中。

HTML 代码

    <span id="days"> </span> 
    <span id="hours"></span>
    <span id="minutes"></span> 
    <span id="seconds"></span>

再简单不过了:)

JAVASCRIPT

 //create two variables for holding the date for 30 back from now using    substract

var back30Days = moment().subtract(30, 'days').format('YYYY-MM-DD H:mm:ss');
   var countDownSeconds = Math.floor(moment().diff(back30Days, 'seconds'));



 //variables holding days, hours , minutes and seconds



  var Days, Minutes, Hours, Seconds;
   // Set Interval function for performing all calculations and decrementing the countDownSeconds 

   setInterval(function () {

   // Updating Days 
   Days = pad(Math.floor(countDownSeconds / 86400), 2);
   // Updating Hours 
   Hours = pad(Math.floor((countDownSeconds - (Days * 86400)) / 3600), 2);
   // Updating Minutes
   Minutes = pad(Math.floor((countDownSeconds - (Days * 86400) - (Hours * 3600)) / 60), 2);
   // Updating Seconds
   Seconds = pad(Math.floor((countDownSeconds - (Days * 86400) - (Hours * 3600) - (Minutes * 60))), 2);

   // Updation our HTML view
   document.getElementById("days").innerHTML = Days + ' Days';
   document.getElementById("hours").innerHTML = Hours + ' Hours';
   document.getElementById("minutes").innerHTML = Minutes + ' Minutes';
   document.getElementById("seconds").innerHTML = Seconds + ' Seconds';

   // Decrement the countDownSeconds
   countDownSeconds--;

   // If we reach zero , our chrono should reset to 30 days back again, as you told
   if (countDownSeconds === 0) {
       countDownSeconds = Math.floor(moment().diff(back30Days, 'seconds'));
   }

   }, 1000);
  

 // Function for padding the seconds i.e limit it only to 2 digits

   function pad(num, size) {
       var s = num + "";
       while (s.length < size) s = "0" + s;
       return s;
   }

Here is a jsfiddle

【讨论】：