HTML5 Audio Tag with Progress

/*Downloaded from https://www.codeseek.co/1Marc/html5-audio-tag-with-progress-jyeEa */
window.onload = function(){
  var myAudio = document.getElementById('my-audio');
  var controlBar = document.getElementById('control-bar');
  
  // we add our listeners
  myAudio.addEventListener('timeupdate', updatePlayed, false);
  myAudio.addEventListener('progress', updateBuffered, false);
  
  function updatePlayed() {
     var played = parseInt(((myAudio.currentTime / myAudio.duration) * 100), 10);
     // gives us a percentage
     addBars(played,'played-bar');
  }
  
  function updateBuffered() {
     var loaded = parseInt(((myAudio.buffered.end(0) / myAudio.duration) * 100), 10);
     // gives us a percentage 
     addBars(loaded,'buffer-bar'); 
  } 
  
  function addBars(amount,element) {
     var bars = "00";
     // since our bars are in increments of 10
     for (i=10; i < 100; i = i + 10) {
        if (i <= amount) {
           bars = bars + " " + i;
        }
     }
  
     var bar = document.getElementById(element);
     bar.innerHTML = bars;
  }
    
  controlBar.onclick = setTime;
  
  function setTime(e) {
    e.preventDefault();
    
    var playPosition = e.target.getAttribute('href'); // from 0 to 90
    myAudio.currentTime = (myAudio.duration * playPosition)/100;
    myAudio.play();
    return false;
  }   

}