index.js

var l = document.querySelectorAll(".drum").length;
for(var i=0;i< l ;i++){
  document.querySelectorAll(".drum")[i].addEventListener("click", function(){

    var buttonText = this.innerHTML;
    makeSound(buttonText);
    buttonAnimation(buttonText);
  });
}
  document.addEventListener("keydown", function(event){
    makeSound(event.key);
    buttonAnimation(event.key);
  });

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

      default: console.log(buttonText);
    }
  }

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

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