function playSound(e) {
  const audio = document.querySelector(`audio[data-key='${e.keyCode}']`);
  const key= document.querySelector(`.key[data-key='${e.keyCode}']`);

  audio.currentTime=0;
  audio.play();
  key.classList.add('playing');
};

const keys = document.querySelectorAll('.key');
keys.forEach(key => key.addEventListener('transitionend', this.classList.remove('playing')));
window.addEventListener('keydown', playSound);