index.js

for(var i =0;i<7;i++){
    document.querySelectorAll("button")[i].addEventListener("click",function (){
        switch(this.textContent){
            case "w":
                var audio = new Audio('./sounds/crash.mp3');
                audio.play();
                break;

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

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

            case "k":
                var audio = new Audio('./sounds/tom-2.mp3');
                audio.play();
                break;
            
            case "j":
                var audio = new Audio('./sounds/tom-3.mp3');
                audio.play();
                break;

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

            default: alert("Error");
        }
        glowButton(this.textContent);
    }
);
}

document.addEventListener("keydown",function(event){
    switch(event.key){
        case "w":
            var audio = new Audio('./sounds/crash.mp3');
            audio.play();
            break;

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

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

        case "k":
            var audio = new Audio('./sounds/tom-2.mp3');
            audio.play();
            break;
        
        case "j":
            var audio = new Audio('./sounds/tom-3.mp3');
            audio.play();
            break;

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

        default: console.log("Error");
    }
    glowButton(event.key);
})

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

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