Hacker News: New Comment Marker

hacker-news-new-comment-marker.user.js

// ==UserScript==
// @name           Hacker News: New Comment Marker
// @description    Make "new" comments since your last visit especially visible
// @downloadURL    https://gist.github.com/noscript/b0420686256ab961e4e3f668bf9f1f5b/raw/hacker-news-new-comment-marker.user.js
// @namespace      https://gist.github.com/noscript
// @grant          GM_addStyle
// @grant          GM_getValue
// @grant          GM_setValue
// @version        3
// @include        https://news.ycombinator.com/item?id=*
// ==/UserScript==

GM_addStyle('.unread { background: #FBFB78; }');
let postId = document.location.href.replace(/.*\?id=/, '');
let oldLatest = GM_getValue(postId, 0);
let newLatest = 0;
Array.from(document.querySelectorAll(".comhead .age")).forEach((el) => {
  let timestamp = Date.parse(el.title);
  if (oldLatest > 0 && timestamp > oldLatest) {
    el.closest('table').classList.add('unread');
  }
  if (timestamp > newLatest) {
    newLatest = timestamp;
  }
});
GM_setValue(postId, newLatest);

Screenshot: