getElementByClassName

/**
 * @param {Element} element
 * @param {string} classNames
 * @return {Array<Element>}
 */
export default function getElementsByClassName(element, classNames) {
  const results = [];

  function traverse(node) {
    if (!node) {
      return;
    }
    // Split target classes into an array for multi-class support
    const targetClasses = classNames.trim().split(/\s+/);

    if (node.nodeType === Node.ELEMENT_NODE) {
      // const hasAllClasses = targetClasses.every(cls => node.classList.contains(cls)); <== current element should not be included
      
      // if (hasAllClasses) {
      //   results.push(node);
      // }
      if (node.children) {
        for (const child of node.children) {
          const hasAllClasses = targetClasses.every(cls => child.classList.contains(cls));
          if (hasAllClasses) {
            results.push(child);
          }
          traverse(child);
        }
      }
    }
  }

  traverse(element);
  return results;
}