polygerrit-ui/app/behaviors/dom-util-behavior/dom-util-behavior.html

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<script>
(function(window) {
  'use strict';

  window.Gerrit = window.Gerrit || {};

  /** @polymerBehavior Gerrit.DomUtilBehavior */
  Gerrit.DomUtilBehavior = {
    /**
     * Are any ancestors of the element (or the element itself) members of the
     * given class.
     * @param {!Element} element
     * @param {string} className
     * @param {Element=} opt_stopElement If provided, stop traversing the
     *     ancestry when the stop element is reached. The stop element's class
     *     is not checked.
     * @return {boolean}
     */
    descendedFromClass(element, className, opt_stopElement) {
      let isDescendant = element.classList.contains(className);
      while (!isDescendant && element.parentElement &&
          (!opt_stopElement || element.parentElement !== opt_stopElement)) {
        isDescendant = element.classList.contains(className);
        element = element.parentElement;
      }
      return isDescendant;
    },
  };
})(window);
</script>