index.js

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

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

    document.querySelectorAll(".drum")[i].addEventListener("click", function(){
        //console.log(this);
        sound(this.innerHTML);
        animation(this.innerHTML);
    });
}

document.addEventListener("keydown", function(event){
    sound(event.key);
    animation(event.key);
});


function sound(key){
    switch(key){
        case "w":
            var audio1 = new Audio("sounds/crash.mp3");
            audio1.play();
            break;
        case "a":
            var audio2 = new Audio("sounds/kick-bass.mp3");
            audio2.play();
            break;
        case "s":
            var audio3 = new Audio("sounds/snare.mp3");
            audio3.play();
            break;
        case "d":
            var audio4 = new Audio("sounds/tom-1.mp3");
            audio4.play();
            break;
        case "j":
            var audio5 = new Audio("sounds/tom-2.mp3");
            audio5.play();
            break;
        case "k":
            var audio6 = new Audio("sounds/tom-3.mp3");
            audio6.play();
            break;
        case "l":
            var audio7 = new Audio("sounds/tom-4.mp3");
            audio7.play();
            break;
        default: console.log(key);
            break;

    }
}

function animation(key){
    document.querySelector("."+key).classList.add("pressed");

    setTimeout(function(){
        document.querySelector("."+key).classList.remove("pressed");
    }, 100);
}