Q:

Add multiple DateTime Duration strings together using JavaScript to get total duration

I have an HTML Table used to generate a Calendar which shows TimeClock entries for each day a user has worked and clocked in and out of the system.  Each day also shows the total time duration for each clock in/out entry. (multiple "timecard punches" can be within the same day)
Simply put I have DateTime style strings which hold a Duration value and I need to add them all together to get a combined duration value.
In a loop this JavaScript variable totalTimeValue will be assigned a duration value as a text string like this 03:31:23 
Add these duration strings together using JavaScript... 
03:31:23
04:21:56
04:08:42
03:31:17
04:10:59
02:48:21
04:26:11
00:00:39
03:41:37

Using JavaScript and jQuery I have this code below which gets the DateTime Duration value as a string in the format 04:21:19 for each timeclock entry.
My JavaScript/jQuery so far...
Demo of it working here: http://codepen.io/jasondavis/pen/GpPPPR?editors=101 
var totalTimeValue = 0;
var totalWeekTimeValue = 0;

// itterate each week which is table row <tr>
$('#timeclock-cal > tbody  > tr').each(function() {
  console.log('=== New Week ===');

  totalWeekTimeValue = 0;

  // get each day which is a table cell <td>
  $(this).find('td').each(function() {
    console.log('== New Day ==');

    // get total time val for each clock in/out on each day which is inside
    // button with CSS class .cal-punch-total-time
    $(this).find('.cal-punch-total-time').each(function() {

      totalTimeValue = $(this).text();

      console.log(totalTimeValue);

      // THIS PART NEEDS YOUR HELP!
      // NEED TO ADD EACH DATETIME STRING TOGETHER FOR TOTAL DURATION VALUES
      totalWeekTimeValue = totalTimeValue+totalWeekTimeValue;

    });

  });

  console.log('= total week time === '+totalWeekTimeValue);
});

full size image

I have no objection to using the MomentJS library http://momentjs.com/ if it can help in this situation however my research so far did not really show any examples doing what I need to do in this question.
In fact all my StackOverflow and Google searches resulted in no examples of adding durations like this in JavaScript!
I did find this MomentJS plugin MomentJS Durations - https://github.com/jsmreese/moment-duration-format

A:

With JQuery and Javascript its easily possible. Please have a look at below code. 

$(document).ready(function(){
    var pad = function(num) { return ("0"+num).slice(-2); }
    var totalSeconds = 0;
    $("li").each(function(){
        var currentDuration = $(this).text();
        currentDuration = currentDuration.split(":");
        var hrs = parseInt(currentDuration[0],10);
        var min = parseInt(currentDuration[1],10);
        var sec = parseInt(currentDuration[2],10);
        var currDurationSec = sec + (60*min) + (60*60*hrs); 
        totalSeconds +=currDurationSec;
    });
    

    var hours = Math.floor(totalSeconds / 3600);
 totalSeconds %= 3600;
 var minutes = Math.floor(totalSeconds / 60);
 var seconds = totalSeconds % 60;
  $(".totalVal").text(pad(hours)+":"+pad(minutes)+":"+pad(seconds));
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<ul>
    <li>03:31:23</li>
    <li>04:21:56</li>
    <li>04:08:42</li>
    <li>03:31:17</li>
    <li>04:10:59</li>
    <li>02:48:21</li>
    <li>04:26:11</li>
    <li>00:00:39</li>
    <li>03:41:37</li>
</ul>

<div id="totalTime">Total Time:<span class="totalVal"></span></div>

