xtabay

function replaceStars(collection) {
  const re = /^(\s*\*\s*){3}$/;

	collection.forEach((elem) => {
    if(elem.innerHTML.match(re)) {
      elem.insertAdjacentHTML('afterend', '<hr>');
      elem.parentNode.removeChild(elem);
    }
  });
}

replaceStars(document.querySelectorAll('.entry-content p'));