index.js

for (var i=0; i< document.querySelectorAll(".drum").length; i++) {
    document.querySelectorAll("button")[i].addEventListener("click", function() {
        var buttonInnerHTML = this.innerHTML   
        makeSound(buttonInnerHTML) 
        buttonAnimation(buttonInnerHTML)
    });
};

document.addEventListener("keydown", function(e) {
    makeSound(e.key);
    buttonAnimation(e.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(buttonInnerHTML);
    }
}

function buttonAnimation(currentKey) {
    var activeButton = document.querySelector("." + currentKey);
    activeButton.classList.add("pressed");
    setTimeout(() => {
        activeButton.classList.remove("pressed");
    }, 100);
}