chore: convert HeaderPrimary to TypeScript (#4052)

framework/core/js/src/forum/components/HeaderPrimary.js → framework/core/js/src/forum/components/HeaderPrimary.tsx

@@ -1,13 +1,14 @@
 import Component from '../../common/Component';
 import ItemList from '../../common/utils/ItemList';
 import listItems from '../../common/helpers/listItems';
+import type Mithril from 'mithril';
 
 /**
  * The `HeaderPrimary` component displays primary header controls. On the
  * default skin, these are shown just to the right of the forum title.
  */
 export default class HeaderPrimary extends Component {
-  view() {
+  view(): JSX.Element {
     return <ul className="Header-controls">{listItems(this.items().toArray())}</ul>;
   }
 
@@ -16,7 +17,8 @@ export default class HeaderPrimary extends Component {
    *
    * @return {ItemList<import('mithril').Children>}
    */
-  items() {
-    return new ItemList();
+
+  items(): ItemList<Mithril.Children> {
+    return new ItemList<Mithril.Children>();
   }
 }