function toggleClass(element, classToToggle, predicate) {

  // This CANNOT use `classList` internally because IE does not support the
  // second parameter to the `classList.toggle()` method! Which is fine because
  // `classList` will be used by the add/remove functions.
  var has = hasClass(element, classToToggle);

  if (typeof predicate === 'function') {
    predicate = predicate(element, classToToggle);
  }

  if (typeof predicate !== 'boolean') {
    predicate = !has;
  }

  // If the necessary class operation matches the current state of the
  // element, no action is required.
  if (predicate === has) {
    return;
  }

  if (predicate) {
    addClass(element, classToToggle);
  } else {
    removeClass(element, classToToggle);
  }

  return element;
}