index.js

// for mouse clicks
var numberOfDrumButtons=document.querySelectorAll(".drum").length;

for(var i=0;i<numberOfDrumButtons;i++)
{
  document.querySelectorAll(".drum")[i].addEventListener("click",function(){
  var buttonInnerHTML=this.innerHTML;

  playsound(buttonInnerHTML);

  animation(buttonInnerHTML);
  });
}

// for keyboard press
document.addEventListener("keydown",function(event){
  var buttonPressed=event.key;

  playsound(buttonPressed);

  animation(buttonPressed);
});

function playsound(check)
{
  switch (check) {

    case "w":
     var tom1=new Audio('sounds/tom-1.mp3');
     tom1.play();
    break;
    case "a":
     var tom2=new Audio('sounds/tom-2.mp3');
     tom2.play();
    break;
    case "s":
     var tom3=new Audio('sounds/tom-3.mp3');
     tom3.play();
    break;
    case "d":
     var tom4=new Audio('sounds/tom-4.mp3');
     tom4.play();
    break;
    case "j":
     var snare=new Audio('sounds/snare.mp3');
     snare.play();
    break;
    case "k":
     var crash=new Audio('sounds/crash.mp3');
     crash.play();
    break;
    case "l":
     var kick=new Audio('sounds/kick-bass.mp3');
     kick.play();
    break;

    default:console.log(check);

  }
}

function animation(key)
{
  var add=document.querySelector("."+ key);
  add.classList.add("pressed");

  setTimeout(function()
{
  add.classList.remove("pressed");
},100);

}