js-addEventListener

gistfile1.txt

window.addEventListener('keydown', (e) => {
    const audio = document.querySelector(`audio[data-key="${e.keyCode}"]`);
    const key = document.querySelector(`.key[data-key="${e.keyCode}"]`);
    if (!audio) return;
    audio.currentTime = 0;
    audio.play();
    key.classList.add('playing');
    key.classList.remove('playing');
    key.classList.toggle('playing');
    key.classList.contains('playing');
});

function removeTransition(e) {
    if (e.propertyName != 'transform') return;
    this.classList.remove('playing');
}
const keys = document.querySelectorAll('.key');
keys.forEach(key => key.addEventListener('transitionend', removeTransition));