4chan-linkify-greentext.user.js

// ==UserScript==
// @name     4chan Linkify Greentext
// @version  1.2
// @include  http://boards.4chan.org/*
// @include  https://boards.4chan.org/*
// @include  http://www.4chan.org/*
// @include  https://www.4chan.org/*
// @grant    none
// @run-at   document-start
// ==/UserScript==
document.onreadystatechange = function () {
    if (document.readyState === "interactive") {
      document.querySelectorAll('span.quote').forEach(quoteSpan => {
          const post = quoteSpan.parentNode;
          const previousThreadUrl = post.querySelector('a[href*="thread"]');
          let threadId = null;
          if (previousThreadUrl) {
              const threadMatch = previousThreadUrl.href.match(/thread\/(\d{9})/);
              if (threadMatch) threadId = threadMatch[1];
          }
          const quoteIds = quoteSpan.textContent.match(/(?<!>)>(\d{9})/g);
          if (quoteIds) {
              quoteSpan.outerHTML = quoteIds.map(id => {
                  const postId = id.slice(1);
                  const linkUrl = threadId ? `/g/thread/${threadId}#p${postId}` : `#p${postId}`;
                  return `<a href="${linkUrl}" class="quotelink">>>${postId}</a>`;
              }).join(' ');
          }
      });
    }
  };