index.js

for( let i = 0 ; i < 7 ; i++ ){
    document.querySelectorAll( "button")[i].addEventListener( "click", function(){
        var z = this.innerHTML ;
        makeSound(z) ;
        buttonAnimation(z);
    }) ;
}

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

   function makeSound( key ){
    switch(key){
     case 'w' : 
          var aud = new Audio('sounds/tom-1.mp3') ;
          aud.play() ;
          break ;
     case 'a' : 
          var aud = new Audio('sounds/tom-2.mp3') ;
          aud.play() ;
          break ;
     case 's' : 
          var aud = new Audio('sounds/tom-3.mp3') ;
          aud.play() ;
          break ;
     case 'd' : 
          var aud = new Audio('sounds/tom-4.mp3') ;
          aud.play() ;
          break ;
     case 'j' : 
          var aud = new Audio('sounds/snare.mp3') ;
          aud.play() ;
          break ;
     case 'k' : 
          var aud = new Audio('sounds/crash.mp3') ;
          aud.play() ;
          break ;
     case 'l' : 
          var aud = new Audio('sounds/kick-bass.mp3') ;
          aud.play() ;
          break ;
     default : 
    }
   }
   function buttonAnimation(currentKey) {
    var activeButton = document.querySelector("." + currentKey);
    activeButton.classList.add("pressed");
   
    setTimeout(function () {
      activeButton.classList.remove("pressed")
    }, 100);
  }