feat: add reading list renderer module

Renders the data file as category-grouped HTML. Pure string builder with
guarded browser wiring so it is unit-testable in Node; escapes all text,
skips invalid entries, and handles duplicate category slugs.

js/reading-list.js

@@ -0,0 +1,111 @@
+/**
+ * Reading list renderer — turns the curated reading list data file into
+ * category-grouped HTML. Pure string builder (no DOM), so it can be unit
+ * tested in Node; the browser wiring at the bottom is guarded accordingly.
+ */
+import { READING_LIST } from "../data/reading-list.js";
+
+/** HTML-escape a value so it is safe to embed in markup. */
+export function escapeHtml(value) {
+  return String(value)
+    .replaceAll("&", "&")
+    .replaceAll("<", "&lt;")
+    .replaceAll(">", "&gt;")
+    .replaceAll('"', "&quot;")
+    .replaceAll("'", "&#39;");
+}
+
+/** True when the value is an absolute http(s) URL. */
+export function isValidUrl(value) {
+  try {
+    const url = new URL(String(value));
+    return url.protocol === "http:" || url.protocol === "https:";
+  } catch {
+    return false;
+  }
+}
+
+/** True when the entry has everything needed to render. */
+export function isValidEntry(entry) {
+  return Boolean(
+    entry &&
+      typeof entry.title === "string" &&
+      entry.title.length > 0 &&
+      isValidUrl(entry.url)
+  );
+}
+
+/**
+ * Group valid entries by category, preserving first-seen category order and
+ * entry order within each category. Entries without a category fall under
+ * "Uncategorized". Invalid entries are skipped.
+ */
+export function groupByCategory(entries) {
+  const groups = new Map();
+  for (const entry of entries) {
+    if (!isValidEntry(entry)) continue;
+    const category = entry.category || "Uncategorized";
+    if (!groups.has(category)) groups.set(category, []);
+    groups.get(category).push(entry);
+  }
+  return groups;
+}
+
+/** Slugify a category name into a stable, unique HTML id. */
+function slugify(value) {
+  return value
+    .toLowerCase()
+    .replace(/[^a-z0-9]+/g, "-")
+    .replace(/^-+|-+$/g, "");
+}
+
+/** Render one entry: a title link plus an optional one-line note. */
+function renderEntry(entry) {
+  const note = entry.note
+    ? `<p class="reading-note">${escapeHtml(entry.note)}</p>`
+    : "";
+  return (
+    `<li class="reading-entry">` +
+    `<a class="reading-link" href="${escapeHtml(entry.url)}">${escapeHtml(entry.title)}</a>` +
+    note +
+    `</li>`
+  );
+}
+
+/**
+ * Render the full reading list as an HTML string, grouped by category.
+ *
+ * @param {Array<{title: string, url: string, note?: string, category?: string}>} entries
+ * @returns {string} HTML string ready to be injected into `#reading-list`
+ */
+export function renderReadingList(entries) {
+  const groups = groupByCategory(entries);
+  if (groups.size === 0) {
+    return '<p class="reading-empty">The reading list is empty.</p>';
+  }
+
+  const usedIds = new Set();
+  const sections = [];
+  for (const [category, items] of groups) {
+    let id = slugify(category) || "category";
+    while (usedIds.has(id)) id = `${id}-${usedIds.size + 1}`;
+    usedIds.add(id);
+
+    sections.push(
+      `<section class="reading-category" aria-labelledby="${id}">` +
+        `<h2 id="${id}">${escapeHtml(category)}</h2>` +
+        `<ul class="reading-list">${items.map(renderEntry).join("")}</ul>` +
+        `</section>`
+    );
+  }
+  return sections.join("");
+}
+
+// Browser-only wiring — render the data file into the page. Guarded so this
+// module stays importable (and testable) in Node.
+if (typeof window !== "undefined" && typeof document !== "undefined") {
+  const container = document.getElementById("reading-list");
+  if (container) {
+    container.innerHTML = renderReadingList(READING_LIST);
+  }
+}