index.js

var len = document.querySelectorAll(".drum").length;
for (var i = 0; i < len; i++) {

    document.querySelectorAll(".drum")[i].addEventListener("click", function () {
        var buttonValue = this.innerHTML;
        play(buttonValue);
        animationGenerator(buttonValue);
    });
}

document.addEventListener("keydown", function (event) {
    play(event.key);
    animationGenerator(event.key);
});



function play(buttonValue) {
    switch (buttonValue) {
        case 'w':
            var tom1 = new Audio("./sounds/tom-1.mp3");
            tom1.play();
            break;

        case 'a':
            var tom2 = new Audio("./sounds/tom-2.mp3");
            tom2.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 '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(buttonValue);
    }
}

function animationGenerator(currentKey) {
    var pressedKey = document.querySelector("." + currentKey);

    pressedKey.classList.add("pressed");

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