index.js

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

}
document.addEventListener("keydown",function(event){
  makeSound(event.key);
  buttonAnimation(event.key);
});
function makeSound(key){
  switch (key) {
    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:

  }
}
function buttonAnimation(currentKey){
  var activeButton = document.querySelector("."+currentKey);
  activeButton.classList.add("pressed");
  setTimeout(function(){
      activeButton.classList.remove("pressed");

  },100);
}