Add an API to show a count in the document title

js/forum/src/components/DiscussionPage.js

@@ -184,6 +184,7 @@ export default class DiscussionPage extends mixin(Component, evented) {
     this.discussion = discussion;
 
     app.setTitle(discussion.title());
+    app.setTitleCount(0);
 
     // When the API responds with a discussion, it will also include a number of
     // posts. Some of these posts are included because they are on the first

js/forum/src/components/IndexPage.js

@@ -96,6 +96,7 @@ export default class IndexPage extends Component {
     };
 
     app.setTitle('');
+    app.setTitleCount(0);
 
     // Work out the difference between the height of this hero and that of the
     // previous hero. Maintain the same scroll position relative to the bottom

js/lib/App.js

@@ -107,6 +107,9 @@ export default class App {
      * @private
      */
     this.requestError = null;
+
+    this.title = '';
+    this.titleCount = 0;
   }
 
   /**
@@ -139,10 +142,29 @@ export default class App {
    * Set the <title> of the page.
    *
    * @param {String} title
+   * @param {Boolean} [separator] Whether or not to separate the given title and
+   *     the forum's title.
    * @public
    */
   setTitle(title) {
-    document.title = (title ? title + ' - ' : '') + this.forum.attribute('title');
+    this.title = title;
+    this.updateTitle();
+  }
+
+  /**
+   * Set a number to display in the <title> of the page.
+   *
+   * @param {Integer} count
+   */
+  setTitleCount(count) {
+    this.titleCount = count;
+    this.updateTitle();
+  }
+
+  updateTitle() {
+    document.title = (this.titleCount ? `(${this.titleCount}) ` : '') +
+      (this.title ? this.title + ' - ' : '') +
+      this.forum.attribute('title');
   }
 
   /**