gistfile1.js

Array.prototype.forEach.call(document.querySelectorAll('#tracks li div'), function(track) {
  track.addEventListener('click', function(e) {
    e.preventDefault();
    var lyrics = e.target.parentNode.querySelector('p');
    lyrics.style.display = lyrics.style.display == 'none'
      ? 'block'
      : 'none';
  });
});

gistfile2.html

<ol id="tracks">
  <li>
    <div>Track one</div>
    <p>Lyrics</p>
  </li>
  <li>
    <div>Track two</div>
    <p>Lyrics...</p>
  </li>
</ol>