index.js

function playSound(char) {
  switch (char) {
    case "w":
      var crash = new Audio('sounds/crash.mp3');
      crash.play();
      break;

    case "a":
      var kick = new Audio('sounds/kick-bass.mp3');
      kick.play();
      break;

    case "s":
      var snare = new Audio('sounds/snare.mp3');
      snare.play();
      break;

    case "d":
      var tom1 = new Audio('sounds/tom-1.mp3');
      tom1.play();
      break;

    case "j":
      var tom2 = new Audio('sounds/tom-2.mp3');
      tom2.play();
      break;

    case "k":
      var tom3 = new Audio('sounds/tom-3.mp3');
      tom3.play();
      break;

    case "l":
      var tom4 = new Audio('sounds/tom-4.mp3');
      tom4.play();
      break;

    default:
      console.log(char);
  }
}

function buttonAnim (currentKey){
  var activeBttn = document.querySelector("." + currentKey);
  activeBttn.classList.add("pressed");
  setTimeout(function(){activeBttn.classList.remove("pressed");}, 100);
}

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

document.addEventListener("keydown", function(event){
  playSound(event.key);
  buttonAnim(event.key);
})