index.js

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

for( i=0; i < numberOfDrums ; i++) {

  document.querySelectorAll(".drum")[i].addEventListener("click",function (){
      var buttonInnerHTML = this.innerHTML;
      makeSound(buttonInnerHTML);
      buttonAnimation(buttonInnerHTML);
      console.log(event);
  });
}
document.addEventListener("keydown",function (event){ makeSound(event.key);  buttonAnimation(event.key); });
  function  buttonAnimation(key) {
    var theButton = document.querySelector("."+key);
    theButton.classList.add("pressed");
    setTimeout(function () {
      theButton.classList.remove("pressed");
    },200);
  }
  function makeSound(key) {

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

      default:

  }

}