diff --git a/src/domain/LogoutViewModel.js b/src/domain/LogoutViewModel.ts
similarity index 76%
rename from src/domain/LogoutViewModel.js
rename to src/domain/LogoutViewModel.ts
index 24ca440e..3edfcad5 100644
--- a/src/domain/LogoutViewModel.js
+++ b/src/domain/LogoutViewModel.ts
@@ -14,11 +14,18 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {ViewModel} from "./ViewModel";
+import {Options, ViewModel} from "./ViewModel";
 import {Client} from "../matrix/Client.js";
 
-export class LogoutViewModel extends ViewModel {
-    constructor(options) {
+type LogoutOptions = { sessionId: string; } & Options;
+
+export class LogoutViewModel extends ViewModel<LogoutOptions> {
+    private _sessionId: string;
+    private _busy: boolean;
+    private _showConfirm: boolean;
+    private _error?: Error;
+
+    constructor(options: LogoutOptions) {
         super(options);
         this._sessionId = options.sessionId;
         this._busy = false;
@@ -26,19 +33,19 @@ export class LogoutViewModel extends ViewModel {
         this._error = undefined;
     }
 
-    get showConfirm() {
+    get showConfirm(): boolean {
         return this._showConfirm;
     }
 
-    get busy() {
+    get busy(): boolean {
         return this._busy;
     }
 
-    get cancelUrl() {
+    get cancelUrl(): string {
         return this.urlCreator.urlForSegment("session", true);
     }
 
-    async logout() {
+    async logout(): Promise<void> {
         this._busy = true;
         this._showConfirm = false;
         this.emitChange("busy");
@@ -53,7 +60,7 @@ export class LogoutViewModel extends ViewModel {
         }
     }
 
-    get status() {
+    get status(): string {
         if (this._error) {
             return this.i18n`Could not log out of device: ${this._error.message}`;
         } else {
diff --git a/src/domain/RootViewModel.js b/src/domain/RootViewModel.js
index 642e43f4..2711cd2f 100644
--- a/src/domain/RootViewModel.js
+++ b/src/domain/RootViewModel.js
@@ -18,7 +18,7 @@ import {Client} from "../matrix/Client.js";
 import {SessionViewModel} from "./session/SessionViewModel.js";
 import {SessionLoadViewModel} from "./SessionLoadViewModel.js";
 import {LoginViewModel} from "./login/LoginViewModel.js";
-import {LogoutViewModel} from "./LogoutViewModel.js";
+import {LogoutViewModel} from "./LogoutViewModel";
 import {SessionPickerViewModel} from "./SessionPickerViewModel.js";
 import {ViewModel} from "./ViewModel";
 
diff --git a/src/domain/SessionPickerViewModel.js b/src/domain/SessionPickerViewModel.js
index 6714e96f..e486c64f 100644
--- a/src/domain/SessionPickerViewModel.js
+++ b/src/domain/SessionPickerViewModel.js
@@ -16,7 +16,7 @@ limitations under the License.
 
 import {SortedArray} from "../observable/index.js";
 import {ViewModel} from "./ViewModel";
-import {avatarInitials, getIdentifierColorNumber} from "./avatar.js";
+import {avatarInitials, getIdentifierColorNumber} from "./avatar";
 
 class SessionItemViewModel extends ViewModel {
     constructor(options, pickerVM) {
diff --git a/src/domain/ViewModel.ts b/src/domain/ViewModel.ts
index 458b2840..cfe22326 100644
--- a/src/domain/ViewModel.ts
+++ b/src/domain/ViewModel.ts
@@ -29,7 +29,7 @@ import type {ILogger} from "../logging/types";
 import type {Navigation} from "./navigation/Navigation";
 import type {URLRouter} from "./navigation/URLRouter";
 
-type Options = {
+export type Options = {
     platform: Platform
     logger: ILogger
     urlCreator: URLRouter
@@ -95,7 +95,7 @@ export class ViewModel<O extends Options = Options> extends EventEmitter<{change
     // 
     // translated string should probably always be bindings, unless we're fine with a refresh when changing the language?
     // we probably are, if we're using routing with a url, we could just refresh.
-    i18n(parts: string[], ...expr: any[]) {
+    i18n(parts: TemplateStringsArray, ...expr: any[]) {
         // just concat for now
         let result = "";
         for (let i = 0; i < parts.length; ++i) {
diff --git a/src/domain/avatar.js b/src/domain/avatar.ts
similarity index 74%
rename from src/domain/avatar.js
rename to src/domain/avatar.ts
index 5b32020b..6f1ef8b0 100644
--- a/src/domain/avatar.js
+++ b/src/domain/avatar.ts
@@ -14,7 +14,10 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-export function avatarInitials(name) {
+import { Platform } from "../platform/web/Platform";
+import { MediaRepository } from "../matrix/net/MediaRepository";
+
+export function avatarInitials(name: string): string {
     let firstChar = name.charAt(0);
     if (firstChar === "!" || firstChar === "@" || firstChar === "#") {
         firstChar = name.charAt(1);
@@ -29,10 +32,10 @@ export function avatarInitials(name) {
  *
  * @return {number}
  */
-function hashCode(str) {
+function hashCode(str: string): number {
     let hash = 0;
-    let i;
-    let chr;
+    let i: number;
+    let chr: number;
     if (str.length === 0) {
         return hash;
     }
@@ -44,11 +47,11 @@ function hashCode(str) {
     return Math.abs(hash);
 }
 
-export function getIdentifierColorNumber(id) {
+export function getIdentifierColorNumber(id: string): number {
     return (hashCode(id) % 8) + 1;
 }
 
-export function getAvatarHttpUrl(avatarUrl, cssSize, platform, mediaRepository) {
+export function getAvatarHttpUrl(avatarUrl: string, cssSize: number, platform: Platform, mediaRepository: MediaRepository): string | null {
     if (avatarUrl) {
         const imageSize = cssSize * platform.devicePixelRatio;
         return mediaRepository.mxcUrlThumbnail(avatarUrl, imageSize, imageSize, "crop");
diff --git a/src/domain/session/leftpanel/BaseTileViewModel.js b/src/domain/session/leftpanel/BaseTileViewModel.js
index e1d6dfff..8f5106bf 100644
--- a/src/domain/session/leftpanel/BaseTileViewModel.js
+++ b/src/domain/session/leftpanel/BaseTileViewModel.js
@@ -15,7 +15,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {avatarInitials, getIdentifierColorNumber, getAvatarHttpUrl} from "../../avatar.js";
+import {avatarInitials, getIdentifierColorNumber, getAvatarHttpUrl} from "../../avatar";
 import {ViewModel} from "../../ViewModel";
 
 const KIND_ORDER = ["roomBeingCreated", "invite", "room"];
diff --git a/src/domain/session/rightpanel/MemberDetailsViewModel.js b/src/domain/session/rightpanel/MemberDetailsViewModel.js
index 8ee50030..b3c8278c 100644
--- a/src/domain/session/rightpanel/MemberDetailsViewModel.js
+++ b/src/domain/session/rightpanel/MemberDetailsViewModel.js
@@ -16,7 +16,7 @@ limitations under the License.
 
 import {ViewModel} from "../../ViewModel";
 import {RoomType} from "../../../matrix/room/common";
-import {avatarInitials, getIdentifierColorNumber, getAvatarHttpUrl} from "../../avatar.js";
+import {avatarInitials, getIdentifierColorNumber, getAvatarHttpUrl} from "../../avatar";
 
 export class MemberDetailsViewModel extends ViewModel {
     constructor(options) {
diff --git a/src/domain/session/rightpanel/MemberTileViewModel.js b/src/domain/session/rightpanel/MemberTileViewModel.js
index 9062ea7d..153c70c8 100644
--- a/src/domain/session/rightpanel/MemberTileViewModel.js
+++ b/src/domain/session/rightpanel/MemberTileViewModel.js
@@ -15,7 +15,7 @@ limitations under the License.
 */
 
 import {ViewModel} from "../../ViewModel";
-import {avatarInitials, getIdentifierColorNumber, getAvatarHttpUrl} from "../../avatar.js";
+import {avatarInitials, getIdentifierColorNumber, getAvatarHttpUrl} from "../../avatar";
 
 export class MemberTileViewModel extends ViewModel {
     constructor(options) {
diff --git a/src/domain/session/rightpanel/RoomDetailsViewModel.js b/src/domain/session/rightpanel/RoomDetailsViewModel.js
index 97e8588e..4e2735b1 100644
--- a/src/domain/session/rightpanel/RoomDetailsViewModel.js
+++ b/src/domain/session/rightpanel/RoomDetailsViewModel.js
@@ -15,7 +15,7 @@ limitations under the License.
 */
 
 import {ViewModel} from "../../ViewModel";
-import {avatarInitials, getIdentifierColorNumber, getAvatarHttpUrl} from "../../avatar.js";
+import {avatarInitials, getIdentifierColorNumber, getAvatarHttpUrl} from "../../avatar";
 
 export class RoomDetailsViewModel extends ViewModel {
     constructor(options) {
diff --git a/src/domain/session/room/InviteViewModel.js b/src/domain/session/room/InviteViewModel.js
index c2ff74e0..00697642 100644
--- a/src/domain/session/room/InviteViewModel.js
+++ b/src/domain/session/room/InviteViewModel.js
@@ -15,7 +15,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {avatarInitials, getIdentifierColorNumber, getAvatarHttpUrl} from "../../avatar.js";
+import {avatarInitials, getIdentifierColorNumber, getAvatarHttpUrl} from "../../avatar";
 import {ViewModel} from "../../ViewModel";
 
 export class InviteViewModel extends ViewModel {
diff --git a/src/domain/session/room/RoomBeingCreatedViewModel.js b/src/domain/session/room/RoomBeingCreatedViewModel.js
index f5c5d3cd..b503af73 100644
--- a/src/domain/session/room/RoomBeingCreatedViewModel.js
+++ b/src/domain/session/room/RoomBeingCreatedViewModel.js
@@ -15,7 +15,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {avatarInitials, getIdentifierColorNumber, getAvatarHttpUrl} from "../../avatar.js";
+import {avatarInitials, getIdentifierColorNumber, getAvatarHttpUrl} from "../../avatar";
 import {ViewModel} from "../../ViewModel";
 
 export class RoomBeingCreatedViewModel extends ViewModel {
diff --git a/src/domain/session/room/RoomViewModel.js b/src/domain/session/room/RoomViewModel.js
index b7af00ce..71060728 100644
--- a/src/domain/session/room/RoomViewModel.js
+++ b/src/domain/session/room/RoomViewModel.js
@@ -17,7 +17,7 @@ limitations under the License.
 
 import {TimelineViewModel} from "./timeline/TimelineViewModel.js";
 import {ComposerViewModel} from "./ComposerViewModel.js"
-import {avatarInitials, getIdentifierColorNumber, getAvatarHttpUrl} from "../../avatar.js";
+import {avatarInitials, getIdentifierColorNumber, getAvatarHttpUrl} from "../../avatar";
 import {tilesCreator} from "./timeline/tilesCreator.js";
 import {ViewModel} from "../../ViewModel";
 import {imageToInfo} from "../common.js";
diff --git a/src/domain/session/room/timeline/MessageBody.js b/src/domain/session/room/timeline/MessageBody.js
index a8bf2497..65b487a9 100644
--- a/src/domain/session/room/timeline/MessageBody.js
+++ b/src/domain/session/room/timeline/MessageBody.js
@@ -1,5 +1,5 @@
 import { linkify } from "./linkify/linkify.js";
-import { getIdentifierColorNumber, avatarInitials } from "../../../avatar.js";
+import { getIdentifierColorNumber, avatarInitials } from "../../../avatar";
 
 /**
  * Parse text into parts such as newline, links and text.
diff --git a/src/domain/session/room/timeline/tiles/BaseMessageTile.js b/src/domain/session/room/timeline/tiles/BaseMessageTile.js
index 6b0b4356..3385a587 100644
--- a/src/domain/session/room/timeline/tiles/BaseMessageTile.js
+++ b/src/domain/session/room/timeline/tiles/BaseMessageTile.js
@@ -16,7 +16,7 @@ limitations under the License.
 
 import {SimpleTile} from "./SimpleTile.js";
 import {ReactionsViewModel} from "../ReactionsViewModel.js";
-import {getIdentifierColorNumber, avatarInitials, getAvatarHttpUrl} from "../../../../avatar.js";
+import {getIdentifierColorNumber, avatarInitials, getAvatarHttpUrl} from "../../../../avatar";
 
 export class BaseMessageTile extends SimpleTile {
     constructor(options) {
diff --git a/src/platform/web/Platform.js b/src/platform/web/Platform.js
index 9de3d4ce..56cf4fc5 100644
--- a/src/platform/web/Platform.js
+++ b/src/platform/web/Platform.js
@@ -37,7 +37,7 @@ import {hasReadPixelPermission, ImageHandle, VideoHandle} from "./dom/ImageHandl
 import {downloadInIframe} from "./dom/download.js";
 import {Disposables} from "../../utils/Disposables";
 import {parseHTML} from "./parsehtml.js";
-import {handleAvatarError} from "./ui/avatar.js";
+import {handleAvatarError} from "./ui/avatar";
 
 function addScript(src) {
     return new Promise(function (resolve, reject) {
diff --git a/src/platform/web/ui/AvatarView.js b/src/platform/web/ui/AvatarView.js
index f2d94e3b..551f7307 100644
--- a/src/platform/web/ui/AvatarView.js
+++ b/src/platform/web/ui/AvatarView.js
@@ -15,7 +15,7 @@ limitations under the License.
 */
 
 import {BaseUpdateView} from "./general/BaseUpdateView";
-import {renderStaticAvatar, renderImg} from "./avatar.js";
+import {renderStaticAvatar, renderImg} from "./avatar";
 
 /*
 optimization to not use a sub view when changing between img and text
diff --git a/src/platform/web/ui/session/room/InviteView.js b/src/platform/web/ui/session/room/InviteView.js
index 9d808abf..99345360 100644
--- a/src/platform/web/ui/session/room/InviteView.js
+++ b/src/platform/web/ui/session/room/InviteView.js
@@ -16,7 +16,7 @@ limitations under the License.
 */
 
 import {TemplateView} from "../../general/TemplateView";
-import {renderStaticAvatar} from "../../avatar.js";
+import {renderStaticAvatar} from "../../avatar";
 
 export class InviteView extends TemplateView {
     render(t, vm) {
diff --git a/src/platform/web/ui/session/room/timeline/BaseMessageView.js b/src/platform/web/ui/session/room/timeline/BaseMessageView.js
index a6fbb9be..9b583103 100644
--- a/src/platform/web/ui/session/room/timeline/BaseMessageView.js
+++ b/src/platform/web/ui/session/room/timeline/BaseMessageView.js
@@ -15,7 +15,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {renderStaticAvatar} from "../../../avatar.js";
+import {renderStaticAvatar} from "../../../avatar";
 import {tag} from "../../../general/html";
 import {mountView} from "../../../general/utils";
 import {TemplateView} from "../../../general/TemplateView";