Calculate total course time for Alibaba Cloud Certificate

courseTotalTime.js

var dates = document.getElementsByClassName("date");
var totalTime = '00:00:00';
for(var i=0;i<dates.length;i++) {
 totalTime = formatTime(timestrToSec(totalTime) + timestrToSec('00:'+dates[i].innerText));
}

console.log("Total Time: "+totalTime);

function timestrToSec(timestr) {
  var parts = timestr.split(":");
  return (parts[0] * 3600) +
         (parts[1] * 60) +
         (+parts[2]);
}

function pad(num) {
  if(num < 10) {
    return "0" + num;
  } else {
    return "" + num;
  }
}

function formatTime(seconds) {
  return [pad(Math.floor(seconds/3600)),
          pad(Math.floor(seconds/60)%60),
          pad(seconds%60),
          ].join(":");
}