Как получить индекс элемента массива

var music = [ 
  '../binary/sounds/music/Strangersbynight.mp3', 
  '../binary/sounds/music/029 E-Type - Russian lullaby.mp3', 
  '../binary/sounds/music/035 Technotronic - This beat is Technotronic.mp3', 
  '../binary/sounds/music/037 Radiorama - Desire.mp3', 
  '../binary/sounds/music/039 Silent circle - Touch in the night.mp3' 
]; 
 
document.addEventListener('DOMContentLoaded', function() { 
  for (var i = 0; i < music.length; i++) { 
    addEventListenerToBtn(i, document.getElementById('btn' + i)) 
  } 
}); 
 
 
function addEventListenerToBtn(index, btn) { 
  btn.addEventListener('click', function() { 
    console.log(music[index]); 
  }); 
};

<button id="btn0">btn0</button> 
<button id="btn1">btn1</button> 
<button id="btn2">btn2</button> 
<button id="btn3">btn3</button> 
<button id="btn4">btn4</button>

var music = [ 
  '../binary/sounds/music/Strangersbynight.mp3', 
  '../binary/sounds/music/029 E-Type - Russian lullaby.mp3', 
  '../binary/sounds/music/035 Technotronic - This beat is Technotronic.mp3', 
  '../binary/sounds/music/037 Radiorama - Desire.mp3', 
  '../binary/sounds/music/039 Silent circle - Touch in the night.mp3' 
]; 
 
function addEventListenerToBtn(index, btn) { 
  btn.addEventListener('click', function() { 
    alert("Download: " + this.innerHTML + "\n\r" +  
          "His id: " + this.getAttribute("data-id")); 
  }); 
}; 
 
function splitName(str) { 
  if (typeof str != "undefined") {   
    return str.split("/"); 
  } 
} 
     
function createBtn(tracks) { 
  if (tracks.length > 0 && tracks) {	 
    for (let i = 0; i < tracks.length; i++) { 
 
      let p = document.createElement('p'), 
          track_name = splitName(tracks[i]); 
 
      p.id = "track-" + i; 
      p.className += "playList"; 
      p.setAttribute("data-id", i); 
      p.innerHTML = track_name[track_name.length-1];     
      document.body.appendChild(p); 
      addEventListenerToBtn(i, document.getElementById("track-" + i));   
    } 
  } 
} 
     
createBtn(music);