Find out the full duration time of a YouTube playlist

gistfile1.js

var list = document.getElementsByClassName('pl-video-time');
var time = 0;

function toS(hms) {
  var a = hms.split(':');
  while (a.length < 3) {
    a.unshift(0);
  }
  var seconds = (+a[0]) * 60 * 60 + (+a[1]) * 60 + (+a[2]);
  return seconds;
}

function toHMS(totalSec) {
  var hours = parseInt( totalSec / 3600 ) % 24;
  var minutes = parseInt( totalSec / 60 ) % 60;
  var seconds = totalSec % 60;
  var result = (hours < 10 ? "0" + hours : hours) + ":" + (minutes < 10 ? "0" + minutes : minutes) + ":" + (seconds  < 10 ? "0" + seconds : seconds);
  return result;
}

function add(item) {
   item = item.getElementsByClassName('timestamp')[0];
   if(!item) return; //deal with private videos and such
   item = item.getElementsByTagName('SPAN')[0];
   var timeString = (item.innerText || item.textContent);
   time += toS(timeString);
}

for (var i = 0; i < list.length; i++) {
  var item = list[i];
  add(item);
}

console.log("The full duration time is: " + toHMS(time));