text: function playSound (e) {
    const audio = document.querySelector(`audio[data-key='${e.keyCode}']`)
    const key = document.querySelector(`div[data-key='${e.keyCode}']`)
  
    if (!audio) return
  
    key.classList.add('playing')
    audio.currentTime = 0
    audio.play()
  }
  
  function removeClass (e) {
    if (e.propertyName !== 'transform') return
    e.target.classList.remove('playing')
  }
  
  const keys = document.querySelectorAll('.key')
  keys.forEach(key => key.addEventListener('transitionend', removeClass))
  window.addEventListener('keydown', playSound)
  