classfinder.js

/**
 *
 * @param {Object} el - A DOM node element
 * @param {String} classname - The class name to search for
 */
function findNode(el = {}, classname = '') {
  if (!el.className) el.className = '';

  // Class will be exact match or space seperated
  const firstOfMany = classname ' ';
  const lastOfMany = ' ' + classname;
  const middle = ' ' + firstOfMany;
  if (el.className === classname 
      || el.className.startsWith(firstOfMany)
      || el.className.endsWith(lastOfMany)
      || el.className.includes(middle)) {
     // Has class, return element
    return el;
  }

  // No class, if we haven't reached top of dom, iterate
  if (el.parentNode) {
    return findNode(el.parentNode, classname);
  } else {
    // we've run out of options
    return null
  }
}