index.js

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

for(var i=0; i<numberOfDrumButtons; i++){

document.querySelectorAll(".drum")[i].addEventListener("click", function() {

var buttonInnerHTML = this.innerHTML
	makeSound(buttonInnerHTML);
	buttonAnimation(buttonInnerHTML);

});
}

document.addEventListener("keydown", function(event) {

	makeSound(event.key);
	buttonAnimation(event.key);
});


function makeSound(key) {

	switch (key) {

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

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

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

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

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

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

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

	default: console.log(buttonInnerHTML);

}

}

function buttonAnimation(currentKey) {

	var activeButton = document.querySelector("." + currentKey);

	activeButton.classList.add("pressed");

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