part.js

const checkHref = (element) => {
  const tag = element.tagName;
  return !(tag === 'A' || tag === 'AREA') || element.href;
};
const onFocus = (event) => {
  if (
    event?.target?.tabIndex > -1 
    && current !== event.target
  ) {
    // skip anchors and areas without href and disabled items
    if (!checkHref(event.target) || event.target.disabled) {
      return;
    }
    current = event.target;
    show(current);
  }
};
const onBlur = (event) => {
  if (event?.target?.tabIndex > -1) {
    // find parent item that can be focusable
    current = current?.parentNode;
    while (current && current.tabIndex < 0) {
      current = current.parentNode;
    }
    if (current === document) {
      current = null;
    }
    // return focus to activeElement
    if (!current && document.activeElement && document.activeElement !== document.body) {
      current = document.activeElement;
    }
    if (current) {
      show(current);
    } else {
      hide();
    }
  }
};