addEventListener Classlist Toggle DOM

const span = document.querySelector("span");
const classes = span.classList;

span.addEventListener('click', function() {
  const result = classes.toggle("c");

  if (result) {
    span.textContent = `'c' added; classList is now "${classes}".`;
  } else {
    span.textContent = `'c' removed; classList is now "${classes}".`;
  }
})
Angry Alligator