index.js

var drumButtons = document.querySelectorAll(".drum").length;

for (var i = 0; i < drumButtons; i++) {
  document.querySelectorAll(".drum")[i].addEventListener("click", handleClick);
}

function handleClick() {
  var buttonInnerHTML = this.innerHTML;
makeSound(buttonInnerHTML);
buttonAnimation(buttonInnerHTML);
}

document.addEventListener("keypress",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 kickbass = new Audio("sounds/kick-bass.mp3");
      kickbass.play();
      break;
    default:
      return;
  }
}

function buttonAnimation(currentkey)
{
  var activeButton=document.querySelector("."+currentkey);

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