Add TopCommentSort.os.js: sort Reddit post comments by Top by default

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

TopCommentSort.os.js

@@ -0,0 +1,61 @@
+// ==UserScript==
+// @name         Top Comment Sort
+// @version      1.0.0
+// @description  Opens every Reddit post with its comments sorted by Top, while still letting you pick another sort.
+// @match        https://www.reddit.com/*
+// @run-at       document_start
+// ==/UserScript==
+
+const POST = /^\/(?:(?:r|u|user)\/[^/]+\/)?comments\/[a-z0-9]+/i;
+const KEY = 'os-top-comment-sort';
+
+// Sorted URL for a post page without an explicit sort, otherwise null
+const sorted = raw => {
+  const url = new URL(raw, location.href);
+  if (url.origin !== location.origin || !POST.test(url.pathname) || url.searchParams.has('sort')) return null;
+  url.searchParams.set('sort', 'top');
+  return url.href;
+};
+
+// One-shot pass for a path, so a page we already handled (or a sort you picked) is left alone on load
+const mark = path => { try { sessionStorage.setItem(KEY, path); } catch {} };
+const passed = () => {
+  try {
+    const hit = sessionStorage.getItem(KEY) === location.pathname;
+    sessionStorage.removeItem(KEY);
+    return hit;
+  } catch { return false; }
+};
+
+// Direct visits: address bar, new tabs, external links
+const start = sorted(location.href);
+if (!passed() && start) {
+  mark(location.pathname);
+  return location.replace(start);
+}
+
+// In-page navigation to another post: go to the sorted URL instead
+navigation.addEventListener('navigate', e => {
+  const url = new URL(e.destination.url);
+  // Same post with a different sort (e.g. the sort dropdown picking Best): respect it
+  if (url.pathname === location.pathname) {
+    if (!url.searchParams.has('sort')) mark(url.pathname);
+    return;
+  }
+  const target = e.navigationType === 'push' && e.cancelable && !e.hashChange
+    && !e.formData && !e.downloadRequest && sorted(url);
+  if (!target) return;
+  e.preventDefault();
+  e.stopImmediatePropagation();
+  const nav = navigation.navigate(target, { state: e.destination.getState(), info: e.info });
+  nav.committed.catch(() => {});
+  nav.finished.catch(() => {});
+});
+
+// Point post links at the sorted URL before they are followed, so the router loads Top directly
+const rewrite = e => {
+  const a = e.composedPath().find(n => n instanceof HTMLAnchorElement && n.href);
+  const target = a && new URL(a.href).pathname !== location.pathname && sorted(a.href);
+  if (target) a.href = target;
+};
+['mousedown', 'click', 'auxclick', 'focusin'].forEach(type => addEventListener(type, rewrite, true));