diff --git a/framework/core/js/src/admin/compat.js b/framework/core/js/src/admin/compat.ts
similarity index 100%
rename from framework/core/js/src/admin/compat.js
rename to framework/core/js/src/admin/compat.ts
diff --git a/framework/core/js/src/common/compat.js b/framework/core/js/src/common/compat.ts
similarity index 98%
rename from framework/core/js/src/common/compat.js
rename to framework/core/js/src/common/compat.ts
index 47cd56cb09..27c5549f90 100644
--- a/framework/core/js/src/common/compat.js
+++ b/framework/core/js/src/common/compat.ts
@@ -1,3 +1,4 @@
+// @ts-expect-error We need to explicitly use the prefix to distinguish between the extend folder.
 import * as extend from './extend.ts';
 import Session from './Session';
 import Store from './Store';
diff --git a/framework/core/js/src/common/components/AlertManager.js b/framework/core/js/src/common/components/AlertManager.js
deleted file mode 100644
index 90aa2e93db..0000000000
--- a/framework/core/js/src/common/components/AlertManager.js
+++ /dev/null
@@ -1,31 +0,0 @@
-import Component from '../Component';
-
-/**
- * The `AlertManager` component provides an area in which `Alert` components can
- * be shown and dismissed.
- */
-export default class AlertManager extends Component {
-  oninit(vnode) {
-    super.oninit(vnode);
-
-    this.state = this.attrs.state;
-  }
-
-  view() {
-    return (
-      <div class="AlertManager">
-        {Object.entries(this.state.getActiveAlerts()).map(([key, alert]) => {
-          const urgent = alert.attrs.type === 'error';
-
-          return (
-            <div class="AlertManager-alert" role="alert" aria-live={urgent ? 'assertive' : 'polite'}>
-              <alert.componentClass {...alert.attrs} ondismiss={this.state.dismiss.bind(this.state, key)}>
-                {alert.children}
-              </alert.componentClass>
-            </div>
-          );
-        })}
-      </div>
-    );
-  }
-}
diff --git a/framework/core/js/src/common/components/AlertManager.tsx b/framework/core/js/src/common/components/AlertManager.tsx
new file mode 100644
index 0000000000..868ad11e15
--- /dev/null
+++ b/framework/core/js/src/common/components/AlertManager.tsx
@@ -0,0 +1,42 @@
+import Component, { ComponentAttrs } from '../Component';
+import AlertManagerState from '../states/AlertManagerState';
+import type Mithril from 'mithril';
+
+export interface IAlertManagerAttrs extends ComponentAttrs {
+  state: AlertManagerState;
+}
+
+/**
+ * The `AlertManager` component provides an area in which `Alert` components can
+ * be shown and dismissed.
+ */
+export default class AlertManager<CustomAttrs extends IAlertManagerAttrs = IAlertManagerAttrs> extends Component<CustomAttrs, AlertManagerState> {
+  oninit(vnode: Mithril.Vnode<CustomAttrs, this>) {
+    super.oninit(vnode);
+
+    this.state = this.attrs.state;
+  }
+
+  view() {
+    const activeAlerts = this.state.getActiveAlerts();
+
+    return (
+      <div class="AlertManager">
+        {Object.keys(activeAlerts)
+          .map(Number)
+          .map((key) => {
+            const alert = activeAlerts[key];
+            const urgent = alert.attrs.type === 'error';
+
+            return (
+              <div class="AlertManager-alert" role="alert" aria-live={urgent ? 'assertive' : 'polite'}>
+                <alert.componentClass {...alert.attrs} ondismiss={this.state.dismiss.bind(this.state, key)}>
+                  {alert.children}
+                </alert.componentClass>
+              </div>
+            );
+          })}
+      </div>
+    );
+  }
+}
diff --git a/framework/core/js/src/common/components/Page.tsx b/framework/core/js/src/common/components/Page.tsx
index 588435d864..b47183d439 100644
--- a/framework/core/js/src/common/components/Page.tsx
+++ b/framework/core/js/src/common/components/Page.tsx
@@ -13,7 +13,7 @@ export interface IPageAttrs {
  *
  * @abstract
  */
-export default abstract class Page<CustomAttrs extends IPageAttrs = IPageAttrs> extends Component<CustomAttrs> {
+export default abstract class Page<CustomAttrs extends IPageAttrs = IPageAttrs, CustomState = undefined> extends Component<CustomAttrs, CustomState> {
   /**
    * A class name to apply to the body while the route is active.
    */
diff --git a/framework/core/js/src/common/states/AlertManagerState.ts b/framework/core/js/src/common/states/AlertManagerState.ts
index f254ea5024..3551d78f40 100644
--- a/framework/core/js/src/common/states/AlertManagerState.ts
+++ b/framework/core/js/src/common/states/AlertManagerState.ts
@@ -6,6 +6,8 @@ import Alert, { AlertAttrs } from '../components/Alert';
  */
 export type AlertIdentifier = number;
 
+export type AlertArray = { [id: AlertIdentifier]: AlertState };
+
 export interface AlertState {
   componentClass: typeof Alert;
   attrs: AlertAttrs;
@@ -13,8 +15,8 @@ export interface AlertState {
 }
 
 export default class AlertManagerState {
-  protected activeAlerts: { [id: number]: AlertState } = {};
-  protected alertId = 0;
+  protected activeAlerts: AlertArray = {};
+  protected alertId: AlertIdentifier = 0;
 
   getActiveAlerts() {
     return this.activeAlerts;
diff --git a/framework/core/js/src/forum/compat.js b/framework/core/js/src/forum/compat.ts
similarity index 100%
rename from framework/core/js/src/forum/compat.js
rename to framework/core/js/src/forum/compat.ts
diff --git a/framework/core/js/src/forum/components/DiscussionsUserPage.js b/framework/core/js/src/forum/components/DiscussionsUserPage.tsx
similarity index 64%
rename from framework/core/js/src/forum/components/DiscussionsUserPage.js
rename to framework/core/js/src/forum/components/DiscussionsUserPage.tsx
index c4f4b056d7..fcba3ab175 100644
--- a/framework/core/js/src/forum/components/DiscussionsUserPage.js
+++ b/framework/core/js/src/forum/components/DiscussionsUserPage.tsx
@@ -1,19 +1,21 @@
-import UserPage from './UserPage';
+import UserPage, { IUserPageAttrs } from './UserPage';
 import DiscussionList from './DiscussionList';
 import DiscussionListState from '../states/DiscussionListState';
+import type Mithril from 'mithril';
+import type User from '../../common/models/User';
 
 /**
  * The `DiscussionsUserPage` component shows a discussion list inside of a user
  * page.
  */
-export default class DiscussionsUserPage extends UserPage {
-  oninit(vnode) {
+export default class DiscussionsUserPage extends UserPage<IUserPageAttrs, DiscussionListState> {
+  oninit(vnode: Mithril.Vnode<IUserPageAttrs, this>) {
     super.oninit(vnode);
 
     this.loadUser(m.route.param('username'));
   }
 
-  show(user) {
+  show(user: User): void {
     super.show(user);
 
     this.state = new DiscussionListState({
diff --git a/framework/core/js/src/forum/components/IndexPage.js b/framework/core/js/src/forum/components/IndexPage.tsx
similarity index 80%
rename from framework/core/js/src/forum/components/IndexPage.js
rename to framework/core/js/src/forum/components/IndexPage.tsx
index a9bd9f3451..e859d6ee7d 100644
--- a/framework/core/js/src/forum/components/IndexPage.js
+++ b/framework/core/js/src/forum/components/IndexPage.tsx
@@ -1,5 +1,5 @@
 import app from '../../forum/app';
-import Page from '../../common/components/Page';
+import Page, { IPageAttrs } from '../../common/components/Page';
 import ItemList from '../../common/utils/ItemList';
 import listItems from '../../common/helpers/listItems';
 import DiscussionList from './DiscussionList';
@@ -11,15 +11,21 @@ import Dropdown from '../../common/components/Dropdown';
 import Button from '../../common/components/Button';
 import LinkButton from '../../common/components/LinkButton';
 import SelectDropdown from '../../common/components/SelectDropdown';
+import extractText from '../../common/utils/extractText';
+import type Mithril from 'mithril';
+import type Discussion from '../../common/models/Discussion';
+
+export interface IIndexPageAttrs extends IPageAttrs {}
 
 /**
  * The `IndexPage` component displays the index page, including the welcome
  * hero, the sidebar, and the discussion list.
  */
-export default class IndexPage extends Page {
+export default class IndexPage<CustomAttrs extends IIndexPageAttrs = IIndexPageAttrs, CustomState = {}> extends Page<CustomAttrs, CustomState> {
   static providesInitialSearch = true;
+  lastDiscussion?: Discussion;
 
-  oninit(vnode) {
+  oninit(vnode: Mithril.Vnode<CustomAttrs, this>) {
     super.oninit(vnode);
 
     // If the user is returning from a discussion page, then take note of which
@@ -37,9 +43,9 @@ export default class IndexPage extends Page {
       app.discussions.clear();
     }
 
-    app.discussions.refreshParams(app.search.params(), m.route.param('page'));
+    app.discussions.refreshParams(app.search.params(), Number(m.route.param('page')));
 
-    app.history.push('index', app.translator.trans('core.forum.header.back_to_index_tooltip'));
+    app.history.push('index', extractText(app.translator.trans('core.forum.header.back_to_index_tooltip')));
 
     this.bodyClass = 'App--index';
     this.scrollTopOnCreate = false;
@@ -68,11 +74,11 @@ export default class IndexPage extends Page {
   }
 
   setTitle() {
-    app.setTitle(app.translator.trans('core.forum.index.meta_title_text'));
+    app.setTitle(extractText(app.translator.trans('core.forum.index.meta_title_text')));
     app.setTitleCount(0);
   }
 
-  oncreate(vnode) {
+  oncreate(vnode: Mithril.VnodeDOM<CustomAttrs, this>) {
     super.oncreate(vnode);
 
     this.setTitle();
@@ -80,11 +86,11 @@ export default class IndexPage extends Page {
     // 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
     // of the hero so that the sidebar doesn't jump around.
-    const oldHeroHeight = app.cache.heroHeight;
+    const oldHeroHeight = app.cache.heroHeight as number;
     const heroHeight = (app.cache.heroHeight = this.$('.Hero').outerHeight() || 0);
-    const scrollTop = app.cache.scrollTop;
+    const scrollTop = app.cache.scrollTop as number;
 
-    $('#app').css('min-height', $(window).height() + heroHeight);
+    $('#app').css('min-height', ($(window).height() || 0) + heroHeight);
 
     // Let browser handle scrolling on page reload.
     if (app.previous.type == null) return;
@@ -104,10 +110,11 @@ export default class IndexPage extends Page {
       const $discussion = this.$(`li[data-id="${this.lastDiscussion.id()}"] .DiscussionListItem`);
 
       if ($discussion.length) {
-        const indexTop = $('#header').outerHeight();
-        const indexBottom = $(window).height();
-        const discussionTop = $discussion.offset().top;
-        const discussionBottom = discussionTop + $discussion.outerHeight();
+        const indexTop = $('#header').outerHeight() || 0;
+        const indexBottom = $(window).height() || 0;
+        const discussionOffset = $discussion.offset();
+        const discussionTop = (discussionOffset && discussionOffset.top) || 0;
+        const discussionBottom = discussionTop + ($discussion.outerHeight() || 0);
 
         if (discussionTop < scrollTop + indexTop || discussionBottom > scrollTop + indexBottom) {
           $(window).scrollTop(discussionTop - indexTop);
@@ -116,7 +123,7 @@ export default class IndexPage extends Page {
     }
   }
 
-  onbeforeremove(vnode) {
+  onbeforeremove(vnode: Mithril.VnodeDOM<CustomAttrs, this>) {
     super.onbeforeremove(vnode);
 
     // Save the scroll position so we can restore it when we return to the
@@ -124,7 +131,7 @@ export default class IndexPage extends Page {
     app.cache.scrollTop = $(window).scrollTop();
   }
 
-  onremove(vnode) {
+  onremove(vnode: Mithril.VnodeDOM<CustomAttrs, this>) {
     super.onremove(vnode);
 
     $('#app').css('min-height', '');
@@ -132,8 +139,6 @@ export default class IndexPage extends Page {
 
   /**
    * Get the component to display as the hero.
-   *
-   * @return {import('mithril').Children}
    */
   hero() {
     return WelcomeHero.component();
@@ -143,11 +148,9 @@ export default class IndexPage extends Page {
    * Build an item list for the sidebar of the index page. By default this is a
    * "New Discussion" button, and then a DropdownSelect component containing a
    * list of navigation items.
-   *
-   * @return {ItemList<import('mithril').Children>}
    */
   sidebarItems() {
-    const items = new ItemList();
+    const items = new ItemList<Mithril.Children>();
     const canStartDiscussion = app.forum.attribute('canStartDiscussion') || !app.session.user;
 
     items.add(
@@ -176,7 +179,7 @@ export default class IndexPage extends Page {
           className: 'App-titleControl',
           accessibleToggleLabel: app.translator.trans('core.forum.index.toggle_sidenav_dropdown_accessible_label'),
         },
-        this.navItems(this).toArray()
+        this.navItems().toArray()
       )
     );
 
@@ -186,11 +189,9 @@ export default class IndexPage extends Page {
   /**
    * Build an item list for the navigation in the sidebar of the index page. By
    * default this is just the 'All Discussions' link.
-   *
-   * @return {ItemList<import('mithril').Children>}
    */
   navItems() {
-    const items = new ItemList();
+    const items = new ItemList<Mithril.Children>();
     const params = app.search.stickyParams();
 
     items.add(
@@ -212,14 +213,12 @@ export default class IndexPage extends Page {
    * Build an item list for the part of the toolbar which is concerned with how
    * the results are displayed. By default this is just a select box to change
    * the way discussions are sorted.
-   *
-   * @return {ItemList<import('mithril').Children>}
    */
   viewItems() {
-    const items = new ItemList();
+    const items = new ItemList<Mithril.Children>();
     const sortMap = app.discussions.sortMap();
 
-    const sortOptions = Object.keys(sortMap).reduce((acc, sortId) => {
+    const sortOptions = Object.keys(sortMap).reduce((acc: any, sortId) => {
       acc[sortId] = app.translator.trans(`core.forum.index_sort.${sortId}_button`);
       return acc;
     }, {});
@@ -254,11 +253,9 @@ export default class IndexPage extends Page {
   /**
    * Build an item list for the part of the toolbar which is about taking action
    * on the results. By default this is just a "mark all as read" button.
-   *
-   * @return {ItemList<import('mithril').Children>}
    */
   actionItems() {
-    const items = new ItemList();
+    const items = new ItemList<Mithril.Children>();
 
     items.add(
       'refresh',
@@ -269,7 +266,7 @@ export default class IndexPage extends Page {
         onclick: () => {
           app.discussions.refresh();
           if (app.session.user) {
-            app.store.find('users', app.session.user.id());
+            app.store.find('users', app.session.user.id()!);
             m.redraw();
           }
         },
@@ -293,10 +290,8 @@ export default class IndexPage extends Page {
 
   /**
    * Open the composer for a new discussion or prompt the user to login.
-   *
-   * @return {Promise<void>}
    */
-  newDiscussionAction() {
+  newDiscussionAction(): Promise<unknown> {
     return new Promise((resolve, reject) => {
       if (app.session.user) {
         app.composer.load(DiscussionComposer, { user: app.session.user });
@@ -315,10 +310,10 @@ export default class IndexPage extends Page {
    * Mark all discussions as read.
    */
   markAllAsRead() {
-    const confirmation = confirm(app.translator.trans('core.forum.index.mark_all_as_read_confirmation'));
+    const confirmation = confirm(extractText(app.translator.trans('core.forum.index.mark_all_as_read_confirmation')));
 
     if (confirmation) {
-      app.session.user.save({ markedAllAsReadAt: new Date() });
+      app.session.user?.save({ markedAllAsReadAt: new Date() });
     }
   }
 }
diff --git a/framework/core/js/src/forum/components/PostsUserPage.js b/framework/core/js/src/forum/components/PostsUserPage.tsx
similarity index 73%
rename from framework/core/js/src/forum/components/PostsUserPage.js
rename to framework/core/js/src/forum/components/PostsUserPage.tsx
index 5c8f1901a8..920a99ec5d 100644
--- a/framework/core/js/src/forum/components/PostsUserPage.js
+++ b/framework/core/js/src/forum/components/PostsUserPage.tsx
@@ -1,46 +1,41 @@
 import app from '../../forum/app';
-import UserPage from './UserPage';
+import UserPage, { IUserPageAttrs } from './UserPage';
 import LoadingIndicator from '../../common/components/LoadingIndicator';
 import Button from '../../common/components/Button';
 import Link from '../../common/components/Link';
 import Placeholder from '../../common/components/Placeholder';
 import CommentPost from './CommentPost';
+import type Post from '../../common/models/Post';
+import type Mithril from 'mithril';
+import type User from '../../common/models/User';
 
 /**
  * The `PostsUserPage` component shows a user's activity feed inside of their
  * profile.
  */
 export default class PostsUserPage extends UserPage {
-  oninit(vnode) {
-    super.oninit(vnode);
+  /**
+   * Whether or not the activity feed is currently loading.
+   */
+  loading: boolean = true;
 
-    /**
-     * Whether or not the activity feed is currently loading.
-     *
-     * @type {Boolean}
-     */
-    this.loading = true;
+  /**
+   * Whether or not there are any more activity items that can be loaded.
+   */
+  moreResults: boolean = false;
 
-    /**
-     * Whether or not there are any more activity items that can be loaded.
-     *
-     * @type {Boolean}
-     */
-    this.moreResults = false;
-
-    /**
-     * The Post models in the feed.
-     *
-     * @type {Post[]}
-     */
-    this.posts = [];
+  /**
+   * The Post models in the feed.
+   */
+  posts: Post[] = [];
 
-    /**
-     * The number of activity items to load per request.
-     *
-     * @type {number}
-     */
-    this.loadLimit = 20;
+  /**
+   * The number of activity items to load per request.
+   */
+  loadLimit: number = 20;
+
+  oninit(vnode: Mithril.Vnode<IUserPageAttrs, this>) {
+    super.oninit(vnode);
 
     this.loadUser(m.route.param('username'));
   }
@@ -92,7 +87,7 @@ export default class PostsUserPage extends UserPage {
    * Initialize the component with a user, and trigger the loading of their
    * activity feed.
    */
-  show(user) {
+  show(user: User): void {
     super.show(user);
 
     this.refresh();
@@ -113,14 +108,12 @@ export default class PostsUserPage extends UserPage {
   /**
    * Load a new page of the user's activity feed.
    *
-   * @param {number} [offset] The position to start getting results from.
-   * @return {Promise<import('../../common/models/Post').default[]>}
    * @protected
    */
-  loadResults(offset) {
-    return app.store.find('posts', {
+  loadResults(offset = 0) {
+    return app.store.find<Post[]>('posts', {
       filter: {
-        author: this.user.username(),
+        author: this.user!.username(),
         type: 'comment',
       },
       page: { offset, limit: this.loadLimit },
@@ -138,11 +131,8 @@ export default class PostsUserPage extends UserPage {
 
   /**
    * Parse results and append them to the activity feed.
-   *
-   * @param {import('../../common/models/Post').default[]} results
-   * @return {import('../../common/models/Post').default[]}
    */
-  parseResults(results) {
+  parseResults(results: Post[]): Post[] {
     this.loading = false;
 
     this.posts.push(...results);
diff --git a/framework/core/js/src/forum/components/UserPage.js b/framework/core/js/src/forum/components/UserPage.tsx
similarity index 81%
rename from framework/core/js/src/forum/components/UserPage.js
rename to framework/core/js/src/forum/components/UserPage.tsx
index 3b4b1863dc..133c936c39 100644
--- a/framework/core/js/src/forum/components/UserPage.js
+++ b/framework/core/js/src/forum/components/UserPage.tsx
@@ -1,5 +1,5 @@
 import app from '../../forum/app';
-import Page from '../../common/components/Page';
+import Page, { IPageAttrs } from '../../common/components/Page';
 import ItemList from '../../common/utils/ItemList';
 import UserCard from './UserCard';
 import LoadingIndicator from '../../common/components/LoadingIndicator';
@@ -8,6 +8,10 @@ import LinkButton from '../../common/components/LinkButton';
 import Separator from '../../common/components/Separator';
 import listItems from '../../common/helpers/listItems';
 import AffixedSidebar from './AffixedSidebar';
+import type User from '../../common/models/User';
+import type Mithril from 'mithril';
+
+export interface IUserPageAttrs extends IPageAttrs {}
 
 /**
  * The `UserPage` component shows a user's profile. It can be extended to show
@@ -16,24 +20,20 @@ import AffixedSidebar from './AffixedSidebar';
  *
  * @abstract
  */
-export default class UserPage extends Page {
-  oninit(vnode) {
-    super.oninit(vnode);
+export default class UserPage<CustomAttrs extends IUserPageAttrs = IUserPageAttrs, CustomState = undefined> extends Page<CustomAttrs, CustomState> {
+  /**
+   * The user this page is for.
+   */
+  user: User | null = null;
 
-    /**
-     * The user this page is for.
-     *
-     * @type {User}
-     */
-    this.user = null;
+  oninit(vnode: Mithril.Vnode<CustomAttrs, this>) {
+    super.oninit(vnode);
 
     this.bodyClass = 'App--user';
   }
 
   /**
    * Base view template for the user page.
-   *
-   * @return {import('mithril').Children}
    */
   view() {
     return (
@@ -64,19 +64,16 @@ export default class UserPage extends Page {
 
   /**
    * Get the content to display in the user page.
-   *
-   * @return {import('mithril').Children}
    */
-  content() {}
+  content(): Mithril.Children | void {}
 
   /**
    * Initialize the component with a user, and trigger the loading of their
    * activity feed.
    *
-   * @param {import('../../common/models/User').default} user
    * @protected
    */
-  show(user) {
+  show(user: User): void {
     this.user = user;
 
     app.current.set('user', user);
@@ -89,10 +86,8 @@ export default class UserPage extends Page {
   /**
    * Given a username, load the user's profile from the store, or make a request
    * if we don't have it yet. Then initialize the profile page with that user.
-   *
-   * @param {string} username
    */
-  loadUser(username) {
+  loadUser(username: string) {
     const lowercaseUsername = username.toLowerCase();
 
     // Load the preloaded user object, if any, into the global app store
@@ -100,25 +95,25 @@ export default class UserPage extends Page {
     // instead of the parsed models
     app.preloadedApiDocument();
 
-    app.store.all('users').some((user) => {
+    app.store.all<User>('users').some((user) => {
       if ((user.username().toLowerCase() === lowercaseUsername || user.id() === username) && user.joinTime()) {
         this.show(user);
         return true;
       }
+
+      return false;
     });
 
     if (!this.user) {
-      app.store.find('users', username, { bySlug: true }).then(this.show.bind(this));
+      app.store.find<User>('users', username, { bySlug: true }).then(this.show.bind(this));
     }
   }
 
   /**
    * Build an item list for the content of the sidebar.
-   *
-   * @return {ItemList<import('mithril').Children>}
    */
   sidebarItems() {
-    const items = new ItemList();
+    const items = new ItemList<Mithril.Children>();
 
     items.add(
       'nav',
@@ -132,12 +127,10 @@ export default class UserPage extends Page {
 
   /**
    * Build an item list for the navigation in the sidebar.
-   *
-   * @return {ItemList<import('mithril').Children>}
    */
   navItems() {
-    const items = new ItemList();
-    const user = this.user;
+    const items = new ItemList<Mithril.Children>();
+    const user = this.user!;
 
     items.add(
       'posts',