Update comments in `annotation-counts` and convert to TS

src/annotator/annotation-counts.js

-const ANNOTATION_COUNT_ATTR = 'data-hypothesis-annotation-count';
-
-/**
- * Update the elements in the container element with the count data attribute
- * with the new annotation count. See:
- * https://h.readthedocs.io/projects/client/en/latest/publishers/host-page-integration/#cmdoption-arg-data-hypothesis-annotation-count
- *
- * @param {Element} rootEl - The DOM element which contains the elements that
- *   display annotation count.
- * @param {import('../shared/messaging').PortRPC<'publicAnnotationCountChanged', string>} rpc - Channel for host-sidebar communication
- */
-export function annotationCounts(rootEl, rpc) {
-  rpc.on('publicAnnotationCountChanged', updateAnnotationCountElems);
-
-  /** @param {number} newCount */
-  function updateAnnotationCountElems(newCount) {
-    const elems = rootEl.querySelectorAll('[' + ANNOTATION_COUNT_ATTR + ']');
-    Array.from(elems).forEach(elem => {
-      elem.textContent = newCount.toString();
-    });
-  }
-}

src/annotator/annotation-counts.ts

+import type { PortRPC } from '../shared/messaging';
+
+const ANNOTATION_COUNT_ATTR = 'data-hypothesis-annotation-count';
+
+/**
+ * Show the current count of public annotations in designated elements.
+ *
+ * Any time the count of public annotations changes, find all elements within
+ * `rootEl` that have the `data-hypothesis-annotation-count` attribute and
+ * replace their text content with the current count of public annotations.
+ *
+ * This allows publishers to add a count of annotations to their web pages.
+ *
+ * See:
+ * https://h.readthedocs.io/projects/client/en/latest/publishers/host-page-integration.html#cmdoption-arg-data-hypothesis-annotation-count
+ *
+ */
+export function annotationCounts(
+  rootEl: Element,
+  rpc: PortRPC<'publicAnnotationCountChanged', string>
+) {
+  rpc.on('publicAnnotationCountChanged', updateAnnotationCountElems);
+
+  function updateAnnotationCountElems(newCount: number) {
+    const elems = rootEl.querySelectorAll(`[${ANNOTATION_COUNT_ATTR}]`);
+    Array.from(elems).forEach(elem => {
+      elem.textContent = newCount.toString();
+    });
+  }
+}