index.js

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

  var buttonLetter = this.innerHTML

  makesound(buttonLetter);//clicked
  buttonAnimation(buttonLetter);
  })
}

document.addEventListener("keypress", function(event){
    makesound(event.key);// specific key that pressed
    buttonAnimation(event.key);
})

function makesound(key){

//the condition bellow allow to identify what is clicked to play a sound.
  switch (key) {
    case "w":
      var tom1 = new Audio ("sounds/tom-1.mp3");
      tom1.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 "a":
      var tom2 = new Audio ("sounds/tom-2.mp3");
      tom2.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: console.log(buttonLetter);

  }
}

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

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