diff --git a/src/domain/LogoutViewModel.ts b/src/domain/LogoutViewModel.ts
index b0409edd..b7aecc2c 100644
--- a/src/domain/LogoutViewModel.ts
+++ b/src/domain/LogoutViewModel.ts
@@ -16,10 +16,11 @@ limitations under the License.
 
 import {Options as BaseOptions, ViewModel} from "./ViewModel";
 import {Client} from "../matrix/Client.js";
+import {SegmentType} from "./navigation/index";
 
 type Options = { sessionId: string; } & BaseOptions;
 
-export class LogoutViewModel extends ViewModel<Options> {
+export class LogoutViewModel extends ViewModel<SegmentType, Options> {
     private _sessionId: string;
     private _busy: boolean;
     private _showConfirm: boolean;
@@ -41,7 +42,7 @@ export class LogoutViewModel extends ViewModel<Options> {
         return this._busy;
     }
 
-    get cancelUrl(): string {
+    get cancelUrl(): string | undefined {
         return this.urlCreator.urlForSegment("session", true);
     }
 
diff --git a/src/domain/ViewModel.ts b/src/domain/ViewModel.ts
index 00ae847b..62da159f 100644
--- a/src/domain/ViewModel.ts
+++ b/src/domain/ViewModel.ts
@@ -27,17 +27,19 @@ import type {Platform} from "../platform/web/Platform";
 import type {Clock} from "../platform/web/dom/Clock";
 import type {ILogger} from "../logging/types";
 import type {Navigation} from "./navigation/Navigation";
-import type {URLRouter} from "./navigation/URLRouter";
+import type {SegmentType} from "./navigation/index";
+import type {IURLRouter} from "./navigation/URLRouter";
 
-export type Options = {
-    platform: Platform
-    logger: ILogger
-    urlCreator: URLRouter
-    navigation: Navigation
-    emitChange?: (params: any) => void
+export type Options<T extends object = SegmentType> = {
+    platform: Platform;
+    logger: ILogger;
+    urlCreator: IURLRouter<T>;
+    navigation: Navigation<T>;
+    emitChange?: (params: any) => void;
 }
 
-export class ViewModel<O extends Options = Options> extends EventEmitter<{change: never}> {
+
+export class ViewModel<N extends object = SegmentType, O extends Options<N> = Options<N>> extends EventEmitter<{change: never}> {
     private disposables?: Disposables;
     private _isDisposed = false;
     private _options: Readonly<O>;
@@ -47,7 +49,7 @@ export class ViewModel<O extends Options = Options> extends EventEmitter<{change
         this._options = options;
     }
 
-    childOptions<T extends Object>(explicitOptions: T): T & Options {
+    childOptions<T extends Object>(explicitOptions: T): T & Options<N> {
         return Object.assign({}, this._options, explicitOptions);
     }
 
@@ -58,9 +60,9 @@ export class ViewModel<O extends Options = Options> extends EventEmitter<{change
         return this._options[name];
     }
 
-    observeNavigation(type: string, onChange: (value: string | true | undefined, type: string) => void): void {
+    observeNavigation<T extends keyof N>(type: T, onChange: (value: N[T], type: T) => void): void {
       const segmentObservable = this.navigation.observe(type);
-      const unsubscribe = segmentObservable.subscribe((value: string | true | undefined) => {
+      const unsubscribe = segmentObservable.subscribe((value: N[T]) => {
         onChange(value, type);
       });
       this.track(unsubscribe);
@@ -135,11 +137,12 @@ export class ViewModel<O extends Options = Options> extends EventEmitter<{change
         return this.platform.logger;
     }
 
-    get urlCreator(): URLRouter {
+    get urlCreator(): IURLRouter<N> {
         return this._options.urlCreator;
     }
 
-    get navigation(): Navigation {
-        return this._options.navigation;
+    get navigation(): Navigation<N> {
+        // typescript needs a little help here
+        return this._options.navigation as unknown as Navigation<N>;
     }
 }
diff --git a/src/domain/login/LoginViewModel.ts b/src/domain/login/LoginViewModel.ts
index aaeca54f..8eb11a9e 100644
--- a/src/domain/login/LoginViewModel.ts
+++ b/src/domain/login/LoginViewModel.ts
@@ -21,6 +21,8 @@ import {StartSSOLoginViewModel} from "./StartSSOLoginViewModel.js";
 import {CompleteSSOLoginViewModel} from "./CompleteSSOLoginViewModel.js";
 import {LoadStatus} from "../../matrix/Client.js";
 import {SessionLoadViewModel} from "../SessionLoadViewModel.js";
+import {SegmentType} from "../navigation/index";
+
 import type {PasswordLoginMethod, SSOLoginHelper, TokenLoginMethod, ILoginMethod} from "../../matrix/login";
 
 type Options = {
@@ -29,7 +31,7 @@ type Options = {
     loginToken?: string;
 } & BaseOptions;
 
-export class LoginViewModel extends ViewModel<Options> {
+export class LoginViewModel extends ViewModel<SegmentType, Options> {
     private _ready: ReadyFn;
     private _loginToken?: string;
     private _client: Client;
diff --git a/src/domain/navigation/Navigation.js b/src/domain/navigation/Navigation.ts
similarity index 65%
rename from src/domain/navigation/Navigation.js
rename to src/domain/navigation/Navigation.ts
index 340ae0d5..f5039732 100644
--- a/src/domain/navigation/Navigation.js
+++ b/src/domain/navigation/Navigation.ts
@@ -16,27 +16,49 @@ limitations under the License.
 
 import {BaseObservableValue, ObservableValue} from "../../observable/ObservableValue";
 
-export class Navigation {
-    constructor(allowsChild) {
+
+type AllowsChild<T> = (parent: Segment<T> | undefined, child: Segment<T>) => boolean;
+
+/**
+ * OptionalValue is basically stating that if SegmentType[type] = true:
+ * - Allow this type to be optional
+ * - Give it a default value of undefined
+ * - Also allow it to be true
+ * This lets us do:
+ * const s: Segment<SegmentType> = new Segment("create-room");
+ * instead of
+ * const s: Segment<SegmentType> = new Segment("create-room", undefined);
+ */
+export type OptionalValue<T> = T extends true? [(undefined | true)?]: [T];
+
+export class Navigation<T extends object> {
+    private readonly _allowsChild: AllowsChild<T>;
+    private _path: Path<T>;
+    private readonly _observables: Map<keyof T, SegmentObservable<T>> = new Map();
+    private readonly _pathObservable: ObservableValue<Path<T>>;
+
+    constructor(allowsChild: AllowsChild<T>) {
         this._allowsChild = allowsChild;
         this._path = new Path([], allowsChild);
-        this._observables = new Map();
         this._pathObservable = new ObservableValue(this._path);
     }
 
-    get pathObservable() {
+    get pathObservable(): ObservableValue<Path<T>> {
         return this._pathObservable;
     }
 
-    get path() {
+    get path(): Path<T> {
         return this._path;
     }
 
-    push(type, value = undefined) {
-        return this.applyPath(this.path.with(new Segment(type, value)));
+    push<K extends keyof T>(type: K, ...value: OptionalValue<T[K]>): void {
+        const newPath = this.path.with(new Segment(type, ...value));
+        if (newPath) {
+            this.applyPath(newPath);
+        }
     }
 
-    applyPath(path) {
+    applyPath(path: Path<T>): void {
         // Path is not exported, so you can only create a Path through Navigation,
         // so we assume it respects the allowsChild rules
         const oldPath = this._path;
@@ -60,7 +82,7 @@ export class Navigation {
         this._pathObservable.set(this._path);
     }
 
-    observe(type) {
+    observe(type: keyof T): SegmentObservable<T> {
         let observable = this._observables.get(type);
         if (!observable) {
             observable = new SegmentObservable(this, type);
@@ -69,9 +91,9 @@ export class Navigation {
         return observable;
     }
 
-    pathFrom(segments) {
-        let parent;
-        let i;
+    pathFrom(segments: Segment<any>[]): Path<T> {
+        let parent: Segment<any> | undefined;
+        let i: number;
         for (i = 0; i < segments.length; i += 1) {
             if (!this._allowsChild(parent, segments[i])) {
                 return new Path(segments.slice(0, i), this._allowsChild);
@@ -81,12 +103,12 @@ export class Navigation {
         return new Path(segments, this._allowsChild);
     }
 
-    segment(type, value) {
-        return new Segment(type, value);
+    segment<K extends keyof T>(type: K, ...value: OptionalValue<T[K]>): Segment<T> {
+        return new Segment(type, ...value);
     }
 }
 
-function segmentValueEqual(a, b) {
+function segmentValueEqual<T>(a?: T[keyof T], b?: T[keyof T]): boolean {
     if (a === b) {
         return true;
     }
@@ -103,24 +125,29 @@ function segmentValueEqual(a, b) {
     return false;
 }
 
-export class Segment {
-    constructor(type, value) {
-        this.type = type;
-        this.value = value === undefined ? true : value;
+
+export class Segment<T, K extends keyof T = any> {
+    public value: T[K];
+
+    constructor(public type: K, ...value: OptionalValue<T[K]>) {
+        this.value = (value[0] === undefined ? true : value[0]) as unknown as T[K];
     }
 }
 
-class Path {
-    constructor(segments = [], allowsChild) {
+class Path<T> {
+    private readonly _segments: Segment<T, any>[];
+    private readonly _allowsChild: AllowsChild<T>;
+
+    constructor(segments: Segment<T>[] = [], allowsChild: AllowsChild<T>) {
         this._segments = segments;
         this._allowsChild = allowsChild;
     }
 
-    clone() {
+    clone(): Path<T> {
         return new Path(this._segments.slice(), this._allowsChild);
     }
 
-    with(segment) {
+    with(segment: Segment<T>): Path<T> | undefined {
         let index = this._segments.length - 1;
         do {
             if (this._allowsChild(this._segments[index], segment)) {
@@ -132,10 +159,10 @@ class Path {
             index -= 1;
         } while(index >= -1);
         // allow -1 as well so we check if the segment is allowed as root
-        return null;
+        return undefined;
     }
 
-    until(type) {
+    until(type: keyof T): Path<T> {
         const index = this._segments.findIndex(s => s.type === type);
         if (index !== -1) {
             return new Path(this._segments.slice(0, index + 1), this._allowsChild)
@@ -143,11 +170,11 @@ class Path {
         return new Path([], this._allowsChild);
     }
 
-    get(type) {
+    get(type: keyof T): Segment<T> | undefined {
         return this._segments.find(s => s.type === type);
     }
 
-    replace(segment) {
+    replace(segment: Segment<T>): Path<T> | undefined {
         const index = this._segments.findIndex(s => s.type === segment.type);
         if (index !== -1) {
             const parent = this._segments[index - 1];
@@ -160,10 +187,10 @@ class Path {
                 }
             }
         }
-        return null;
+        return undefined;
     }
 
-    get segments() {
+    get segments(): Segment<T>[] {
         return this._segments;
     }
 }
@@ -172,43 +199,49 @@ class Path {
  * custom observable so it always returns what is in navigation.path, even if we haven't emitted the change yet.
  * This ensures that observers of a segment can also read the most recent value of other segments.
  */
-class SegmentObservable extends BaseObservableValue {
-    constructor(navigation, type) {
+class SegmentObservable<T extends object> extends BaseObservableValue<T[keyof T] | undefined> {
+    private readonly _navigation: Navigation<T>;
+    private _type: keyof T;
+    private _lastSetValue?: T[keyof T];
+        
+    constructor(navigation: Navigation<T>, type: keyof T) {
         super();
         this._navigation = navigation;
         this._type = type;
         this._lastSetValue = navigation.path.get(type)?.value;
     }
 
-    get() {
+    get(): T[keyof T] | undefined {
         const path = this._navigation.path;
         const segment = path.get(this._type);
         const value = segment?.value;
         return value;
     }
 
-    emitIfChanged() {
+    emitIfChanged(): void {
         const newValue = this.get();
-        if (!segmentValueEqual(newValue, this._lastSetValue)) {
+        if (!segmentValueEqual<T>(newValue, this._lastSetValue)) {
             this._lastSetValue = newValue;
             this.emit(newValue);
         }
     }
 }
 
+export type {Path};
+
 export function tests() {
 
     function createMockNavigation() {
         return new Navigation((parent, {type}) => {
             switch (parent?.type) {
                 case undefined:
-                    return type === "1" || "2";
+                    return type === "1" || type === "2";
                 case "1":
                     return type === "1.1";
                 case "1.1":
                     return type === "1.1.1";
                 case "2":
-                    return type === "2.1" || "2.2";
+                    return type === "2.1" || type === "2.2";
                 default:
                     return false;
             }
@@ -216,7 +249,7 @@ export function tests() {
     }
 
     function observeTypes(nav, types) {
-        const changes = [];
+        const changes: {type:string, value:any}[] = [];
         for (const type of types) {
             nav.observe(type).subscribe(value => {
                 changes.push({type, value});
@@ -225,6 +258,12 @@ export function tests() {
         return changes;
     }
 
+    type SegmentType = {
+        "foo": number;
+        "bar": number;
+        "baz": number;
+    }
+
     return {
         "applying a path emits an event on the observable": assert => {
             const nav = createMockNavigation();
@@ -242,18 +281,18 @@ export function tests() {
             assert.equal(changes[1].value, 8);
         },
         "path.get": assert => {
-            const path = new Path([new Segment("foo", 5), new Segment("bar", 6)], () => true);
-            assert.equal(path.get("foo").value, 5);
-            assert.equal(path.get("bar").value, 6);
+            const path = new Path<SegmentType>([new Segment("foo", 5), new Segment("bar", 6)], () => true);
+            assert.equal(path.get("foo")!.value, 5);
+            assert.equal(path.get("bar")!.value, 6);
         },
         "path.replace success": assert => {
-            const path = new Path([new Segment("foo", 5), new Segment("bar", 6)], () => true);
+            const path = new Path<SegmentType>([new Segment("foo", 5), new Segment("bar", 6)], () => true);
             const newPath = path.replace(new Segment("foo", 1));
-            assert.equal(newPath.get("foo").value, 1);
-            assert.equal(newPath.get("bar").value, 6);
+            assert.equal(newPath!.get("foo")!.value, 1);
+            assert.equal(newPath!.get("bar")!.value, 6);
         },
         "path.replace not found": assert => {
-            const path = new Path([new Segment("foo", 5), new Segment("bar", 6)], () => true);
+            const path = new Path<SegmentType>([new Segment("foo", 5), new Segment("bar", 6)], () => true);
             const newPath = path.replace(new Segment("baz", 1));
             assert.equal(newPath, null);
         }
diff --git a/src/domain/navigation/URLRouter.js b/src/domain/navigation/URLRouter.ts
similarity index 58%
rename from src/domain/navigation/URLRouter.js
rename to src/domain/navigation/URLRouter.ts
index ab5dc5ce..bf1c218d 100644
--- a/src/domain/navigation/URLRouter.js
+++ b/src/domain/navigation/URLRouter.ts
@@ -14,28 +14,55 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-export class URLRouter {
-    constructor({history, navigation, parseUrlPath, stringifyPath}) {
+import type {History} from "../../platform/web/dom/History.js";
+import type {Navigation, Segment, Path, OptionalValue} from "./Navigation";
+import type {SubscriptionHandle} from "../../observable/BaseObservable";
+
+type ParseURLPath<T> = (urlPath: string, currentNavPath: Path<T>, defaultSessionId?: string) => Segment<T>[];
+type StringifyPath<T> = (path: Path<T>) => string;
+
+export interface IURLRouter<T> {
+    attach(): void;
+    dispose(): void;
+    pushUrl(url: string): void;
+    tryRestoreLastUrl(): boolean;
+    urlForSegments(segments: Segment<T>[]): string | undefined;
+    urlForSegment<K extends keyof T>(type: K, ...value: OptionalValue<T[K]>): string | undefined;
+    urlUntilSegment(type: keyof T): string;
+    urlForPath(path: Path<T>): string;
+    openRoomActionUrl(roomId: string): string;
+    createSSOCallbackURL(): string;
+    normalizeUrl(): void;
+}
+
+export class URLRouter<T extends {session: string | boolean}> implements IURLRouter<T> {
+    private readonly _history: History;
+    private readonly _navigation: Navigation<T>;
+    private readonly _parseUrlPath: ParseURLPath<T>;
+    private readonly _stringifyPath: StringifyPath<T>;
+    private _subscription?: SubscriptionHandle;
+    private _pathSubscription?: SubscriptionHandle;
+    private _isApplyingUrl: boolean = false;
+    private _defaultSessionId?: string;
+
+    constructor(history: History, navigation: Navigation<T>, parseUrlPath: ParseURLPath<T>, stringifyPath: StringifyPath<T>) {
         this._history = history;
         this._navigation = navigation;
         this._parseUrlPath = parseUrlPath;
         this._stringifyPath = stringifyPath;
-        this._subscription = null;
-        this._pathSubscription = null;
-        this._isApplyingUrl = false;
         this._defaultSessionId = this._getLastSessionId();
     }
 
-    _getLastSessionId() {
+    private _getLastSessionId(): string | undefined {
         const navPath = this._urlAsNavPath(this._history.getLastSessionUrl() || "");
         const sessionId = navPath.get("session")?.value;
         if (typeof sessionId === "string") {
             return sessionId;
         }
-        return null;
+        return undefined;
     }
 
-    attach() {
+    attach(): void {
         this._subscription = this._history.subscribe(url => this._applyUrl(url));
         // subscribe to path before applying initial url
         // so redirects in _applyNavPathToHistory are reflected in url bar
@@ -43,12 +70,12 @@ export class URLRouter {
         this._applyUrl(this._history.get());
     }
 
-    dispose() {
-        this._subscription = this._subscription();
-        this._pathSubscription = this._pathSubscription();
+    dispose(): void {
+        if (this._subscription) { this._subscription = this._subscription(); }
+        if (this._pathSubscription) { this._pathSubscription = this._pathSubscription(); }
     }
 
-    _applyNavPathToHistory(path) {
+    private _applyNavPathToHistory(path: Path<T>): void {
         const url = this.urlForPath(path);
         if (url !== this._history.get()) {
             if (this._isApplyingUrl) {
@@ -60,7 +87,7 @@ export class URLRouter {
         }
     }
 
-    _applyNavPathToNavigation(navPath) {
+    private _applyNavPathToNavigation(navPath: Path<T>): void {
         // this will cause _applyNavPathToHistory to be called,
         // so set a flag whether this request came from ourselves
         // (in which case it is a redirect if the url does not match the current one)
@@ -69,21 +96,21 @@ export class URLRouter {
         this._isApplyingUrl = false;
     }
 
-    _urlAsNavPath(url) {
+    private _urlAsNavPath(url: string): Path<T> {
         const urlPath = this._history.urlAsPath(url);
         return this._navigation.pathFrom(this._parseUrlPath(urlPath, this._navigation.path, this._defaultSessionId));
     }
 
-    _applyUrl(url) {
+    private _applyUrl(url: string): void {
         const navPath = this._urlAsNavPath(url);
         this._applyNavPathToNavigation(navPath);
     }
 
-    pushUrl(url) {
+    pushUrl(url: string): void {
         this._history.pushUrl(url);
     }
 
-    tryRestoreLastUrl() {
+    tryRestoreLastUrl(): boolean {
         const lastNavPath = this._urlAsNavPath(this._history.getLastSessionUrl() || "");
         if (lastNavPath.segments.length !== 0) {
             this._applyNavPathToNavigation(lastNavPath);
@@ -92,8 +119,8 @@ export class URLRouter {
         return false;
     }
 
-    urlForSegments(segments) {
-        let path = this._navigation.path;
+    urlForSegments(segments: Segment<T>[]): string | undefined {
+        let path: Path<T> | undefined = this._navigation.path;
         for (const segment of segments) {
             path = path.with(segment);
             if (!path) {
@@ -103,29 +130,29 @@ export class URLRouter {
         return this.urlForPath(path);
     }
 
-    urlForSegment(type, value) {
-        return this.urlForSegments([this._navigation.segment(type, value)]);
+    urlForSegment<K extends keyof T>(type: K, ...value: OptionalValue<T[K]>): string | undefined {
+        return this.urlForSegments([this._navigation.segment(type, ...value)]);
     }
 
-    urlUntilSegment(type) {
+    urlUntilSegment(type: keyof T): string {
         return this.urlForPath(this._navigation.path.until(type));
     }
 
-    urlForPath(path) {
+    urlForPath(path: Path<T>): string {
         return this._history.pathAsUrl(this._stringifyPath(path));
     }
 
-    openRoomActionUrl(roomId) {
+    openRoomActionUrl(roomId: string): string {
         // not a segment to navigation knowns about, so append it manually
         const urlPath = `${this._stringifyPath(this._navigation.path.until("session"))}/open-room/${roomId}`;
         return this._history.pathAsUrl(urlPath);
     }
 
-    createSSOCallbackURL() {
+    createSSOCallbackURL(): string {
         return window.location.origin;
     }
 
-    normalizeUrl() {
+    normalizeUrl(): void {
         // Remove any queryParameters from the URL
         // Gets rid of the loginToken after SSO
         this._history.replaceUrlSilently(`${window.location.origin}/${window.location.hash}`);
diff --git a/src/domain/navigation/index.js b/src/domain/navigation/index.ts
similarity index 73%
rename from src/domain/navigation/index.js
rename to src/domain/navigation/index.ts
index 086367ce..afba0d86 100644
--- a/src/domain/navigation/index.js
+++ b/src/domain/navigation/index.ts
@@ -14,18 +14,36 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {Navigation, Segment} from "./Navigation.js";
-import {URLRouter} from "./URLRouter.js";
+import {Navigation, Segment} from "./Navigation";
+import {URLRouter} from "./URLRouter";
+import type {Path, OptionalValue} from "./Navigation";
 
-export function createNavigation() {
+export type SegmentType = {
+    "login": true;
+    "session": string | boolean;
+    "sso": string;
+    "logout": true;
+    "room": string;
+    "rooms": string[];
+    "settings": true;
+    "create-room": true;
+    "empty-grid-tile": number;
+    "lightbox": string;
+    "right-panel": true;
+    "details": true;
+    "members": true;
+    "member": string;
+};
+
+export function createNavigation(): Navigation<SegmentType> {
     return new Navigation(allowsChild);
 }
 
-export function createRouter({history, navigation}) {
-    return new URLRouter({history, navigation, stringifyPath, parseUrlPath});
+export function createRouter({history, navigation}: {history: History, navigation: Navigation<SegmentType>}): URLRouter<SegmentType> {
+    return new URLRouter(history, navigation, parseUrlPath, stringifyPath);
 }
 
-function allowsChild(parent, child) {
+function allowsChild(parent: Segment<SegmentType> | undefined, child: Segment<SegmentType>): boolean {
     const {type} = child;
     switch (parent?.type) {
         case undefined:
@@ -45,8 +63,9 @@ function allowsChild(parent, child) {
     }
 }
 
-export function removeRoomFromPath(path, roomId) {
-    const rooms = path.get("rooms");
+export function removeRoomFromPath(path: Path<SegmentType>, roomId: string): Path<SegmentType> | undefined {
+    let newPath: Path<SegmentType> | undefined = path;
+    const rooms = newPath.get("rooms");
     let roomIdGridIndex = -1;
     // first delete from rooms segment
     if (rooms) {
@@ -54,22 +73,22 @@ export function removeRoomFromPath(path, roomId) {
         if (roomIdGridIndex !== -1) {
             const idsWithoutRoom = rooms.value.slice();
             idsWithoutRoom[roomIdGridIndex] = "";
-            path = path.replace(new Segment("rooms", idsWithoutRoom));
+            newPath = newPath.replace(new Segment("rooms", idsWithoutRoom));
         }
     }
-    const room = path.get("room");
+    const room = newPath!.get("room");
     // then from room (which occurs with or without rooms)
     if (room && room.value === roomId) {
         if (roomIdGridIndex !== -1) {
-            path = path.with(new Segment("empty-grid-tile", roomIdGridIndex));
+            newPath = newPath!.with(new Segment("empty-grid-tile", roomIdGridIndex));
         } else {
-            path = path.until("session");
+            newPath = newPath!.until("session");
         }
     }
-    return path;
+    return newPath;
 }
 
-function roomsSegmentWithRoom(rooms, roomId, path) {
+function roomsSegmentWithRoom(rooms: Segment<SegmentType, "rooms">, roomId: string, path: Path<SegmentType>): Segment<SegmentType, "rooms"> {
     if(!rooms.value.includes(roomId)) {
         const emptyGridTile = path.get("empty-grid-tile");
         const oldRoom = path.get("room");
@@ -87,28 +106,28 @@ function roomsSegmentWithRoom(rooms, roomId, path) {
     }
 }
 
-function pushRightPanelSegment(array, segment, value = true) {
+function pushRightPanelSegment<T extends keyof SegmentType>(array: Segment<SegmentType>[], segment: T, ...value: OptionalValue<SegmentType[T]>): void {
     array.push(new Segment("right-panel"));
-    array.push(new Segment(segment, value));
+    array.push(new Segment(segment, ...value));
 }
 
-export function addPanelIfNeeded(navigation, path) {
+export function addPanelIfNeeded<T extends SegmentType>(navigation: Navigation<T>, path: Path<T>): Path<T> {
     const segments = navigation.path.segments;
     const i = segments.findIndex(segment => segment.type === "right-panel");
     let _path = path;
     if (i !== -1) {
         _path = path.until("room");
-        _path = _path.with(segments[i]);
-        _path = _path.with(segments[i + 1]);
+        _path = _path.with(segments[i])!;
+        _path = _path.with(segments[i + 1])!;
     }
     return _path;
 }
 
-export function parseUrlPath(urlPath, currentNavPath, defaultSessionId) {
-    // substr(1) to take of initial /
-    const parts = urlPath.substr(1).split("/");
+export function parseUrlPath(urlPath: string, currentNavPath: Path<SegmentType>, defaultSessionId?: string): Segment<SegmentType>[] {
+    // substring(1) to take of initial /
+    const parts = urlPath.substring(1).split("/");
     const iterator = parts[Symbol.iterator]();
-    const segments = [];
+    const segments: Segment<SegmentType>[] = [];
     let next; 
     while (!(next = iterator.next()).done) {
         const type = next.value;
@@ -170,9 +189,9 @@ export function parseUrlPath(urlPath, currentNavPath, defaultSessionId) {
     return segments;
 }
 
-export function stringifyPath(path) {
+export function stringifyPath(path: Path<SegmentType>): string {
     let urlPath = "";
-    let prevSegment;
+    let prevSegment: Segment<SegmentType> | undefined;
     for (const segment of path.segments) {
         switch (segment.type) {
             case "rooms":
@@ -205,9 +224,15 @@ export function stringifyPath(path) {
 }
 
 export function tests() {
+    function createEmptyPath() {
+        const nav: Navigation<SegmentType> = new Navigation(allowsChild);
+        const path = nav.pathFrom([]);
+        return path;
+    }
+
     return {
         "stringify grid url with focused empty tile": assert => {
-            const nav = new Navigation(allowsChild);
+            const nav: Navigation<SegmentType> = new Navigation(allowsChild);
             const path = nav.pathFrom([
                 new Segment("session", 1),
                 new Segment("rooms", ["a", "b", "c"]),
@@ -217,7 +242,7 @@ export function tests() {
             assert.equal(urlPath, "/session/1/rooms/a,b,c/3");
         },
         "stringify grid url with focused room": assert => {
-            const nav = new Navigation(allowsChild);
+            const nav: Navigation<SegmentType> = new Navigation(allowsChild);
             const path = nav.pathFrom([
                 new Segment("session", 1),
                 new Segment("rooms", ["a", "b", "c"]),
@@ -227,7 +252,7 @@ export function tests() {
             assert.equal(urlPath, "/session/1/rooms/a,b,c/1");
         },
         "stringify url with right-panel and details segment": assert => {
-            const nav = new Navigation(allowsChild);
+            const nav: Navigation<SegmentType> = new Navigation(allowsChild);
             const path = nav.pathFrom([
                 new Segment("session", 1),
                 new Segment("rooms", ["a", "b", "c"]),
@@ -239,13 +264,15 @@ export function tests() {
             assert.equal(urlPath, "/session/1/rooms/a,b,c/1/details");
         },
         "Parse loginToken query parameter into SSO segment": assert => {
-            const segments = parseUrlPath("?loginToken=a1232aSD123");
+            const path = createEmptyPath();
+            const segments = parseUrlPath("?loginToken=a1232aSD123", path);
             assert.equal(segments.length, 1);
             assert.equal(segments[0].type, "sso");
             assert.equal(segments[0].value, "a1232aSD123");
         },
         "parse grid url path with focused empty tile": assert => {
-            const segments = parseUrlPath("/session/1/rooms/a,b,c/3");
+            const path = createEmptyPath();
+            const segments = parseUrlPath("/session/1/rooms/a,b,c/3", path);
             assert.equal(segments.length, 3);
             assert.equal(segments[0].type, "session");
             assert.equal(segments[0].value, "1");
@@ -255,7 +282,8 @@ export function tests() {
             assert.equal(segments[2].value, 3);
         },
         "parse grid url path with focused room": assert => {
-            const segments = parseUrlPath("/session/1/rooms/a,b,c/1");
+            const path = createEmptyPath();
+            const segments = parseUrlPath("/session/1/rooms/a,b,c/1", path);
             assert.equal(segments.length, 3);
             assert.equal(segments[0].type, "session");
             assert.equal(segments[0].value, "1");
@@ -265,7 +293,8 @@ export function tests() {
             assert.equal(segments[2].value, "b");
         },
         "parse empty grid url": assert => {
-            const segments = parseUrlPath("/session/1/rooms/");
+            const path = createEmptyPath();
+            const segments = parseUrlPath("/session/1/rooms/", path);
             assert.equal(segments.length, 3);
             assert.equal(segments[0].type, "session");
             assert.equal(segments[0].value, "1");
@@ -275,7 +304,8 @@ export function tests() {
             assert.equal(segments[2].value, 0);
         },
         "parse empty grid url with focus": assert => {
-            const segments = parseUrlPath("/session/1/rooms//1");
+            const path = createEmptyPath();
+            const segments = parseUrlPath("/session/1/rooms//1", path);
             assert.equal(segments.length, 3);
             assert.equal(segments[0].type, "session");
             assert.equal(segments[0].value, "1");
@@ -285,7 +315,7 @@ export function tests() {
             assert.equal(segments[2].value, 1);
         },
         "parse open-room action replacing the current focused room": assert => {
-            const nav = new Navigation(allowsChild);
+            const nav: Navigation<SegmentType> = new Navigation(allowsChild);
             const path = nav.pathFrom([
                 new Segment("session", 1),
                 new Segment("rooms", ["a", "b", "c"]),
@@ -301,7 +331,7 @@ export function tests() {
             assert.equal(segments[2].value, "d");
         },
         "parse open-room action changing focus to an existing room": assert => {
-            const nav = new Navigation(allowsChild);
+            const nav: Navigation<SegmentType> = new Navigation(allowsChild);
             const path = nav.pathFrom([
                 new Segment("session", 1),
                 new Segment("rooms", ["a", "b", "c"]),
@@ -317,7 +347,7 @@ export function tests() {
             assert.equal(segments[2].value, "a");
         },
         "parse open-room action changing focus to an existing room with details open": assert => {
-            const nav = new Navigation(allowsChild);
+            const nav: Navigation<SegmentType> = new Navigation(allowsChild);
             const path = nav.pathFrom([
                 new Segment("session", 1),
                 new Segment("rooms", ["a", "b", "c"]),
@@ -339,7 +369,7 @@ export function tests() {
             assert.equal(segments[4].value, true);
         },
         "open-room action should only copy over previous segments if there are no parts after open-room": assert => {
-            const nav = new Navigation(allowsChild);
+            const nav: Navigation<SegmentType> = new Navigation(allowsChild);
             const path = nav.pathFrom([
                 new Segment("session", 1),
                 new Segment("rooms", ["a", "b", "c"]),
@@ -361,7 +391,7 @@ export function tests() {
             assert.equal(segments[4].value, "foo");
         },
         "parse open-room action setting a room in an empty tile": assert => {
-            const nav = new Navigation(allowsChild);
+            const nav: Navigation<SegmentType> = new Navigation(allowsChild);
             const path = nav.pathFrom([
                 new Segment("session", 1),
                 new Segment("rooms", ["a", "b", "c"]),
@@ -377,82 +407,83 @@ export function tests() {
             assert.equal(segments[2].value, "d");
         },
         "parse session url path without id": assert => {
-            const segments = parseUrlPath("/session");
+            const path = createEmptyPath();
+            const segments = parseUrlPath("/session", path);
             assert.equal(segments.length, 1);
             assert.equal(segments[0].type, "session");
             assert.strictEqual(segments[0].value, true);
         },
         "remove active room from grid path turns it into empty tile": assert => {
-            const nav = new Navigation(allowsChild);
+            const nav: Navigation<SegmentType> = new Navigation(allowsChild);
             const path = nav.pathFrom([
                 new Segment("session", 1),
                 new Segment("rooms", ["a", "b", "c"]),
                 new Segment("room", "b")
             ]);
             const newPath = removeRoomFromPath(path, "b");
-            assert.equal(newPath.segments.length, 3);
-            assert.equal(newPath.segments[0].type, "session");
-            assert.equal(newPath.segments[0].value, 1);
-            assert.equal(newPath.segments[1].type, "rooms");
-            assert.deepEqual(newPath.segments[1].value, ["a", "", "c"]);
-            assert.equal(newPath.segments[2].type, "empty-grid-tile");
-            assert.equal(newPath.segments[2].value, 1);
+            assert.equal(newPath?.segments.length, 3);
+            assert.equal(newPath?.segments[0].type, "session");
+            assert.equal(newPath?.segments[0].value, 1);
+            assert.equal(newPath?.segments[1].type, "rooms");
+            assert.deepEqual(newPath?.segments[1].value, ["a", "", "c"]);
+            assert.equal(newPath?.segments[2].type, "empty-grid-tile");
+            assert.equal(newPath?.segments[2].value, 1);
         },
         "remove inactive room from grid path": assert => {
-            const nav = new Navigation(allowsChild);
+            const nav: Navigation<SegmentType> = new Navigation(allowsChild);
             const path = nav.pathFrom([
                 new Segment("session", 1),
                 new Segment("rooms", ["a", "b", "c"]),
                 new Segment("room", "b")
             ]);
             const newPath = removeRoomFromPath(path, "a");
-            assert.equal(newPath.segments.length, 3);
-            assert.equal(newPath.segments[0].type, "session");
-            assert.equal(newPath.segments[0].value, 1);
-            assert.equal(newPath.segments[1].type, "rooms");
-            assert.deepEqual(newPath.segments[1].value, ["", "b", "c"]);
-            assert.equal(newPath.segments[2].type, "room");
-            assert.equal(newPath.segments[2].value, "b");
+            assert.equal(newPath?.segments.length, 3);
+            assert.equal(newPath?.segments[0].type, "session");
+            assert.equal(newPath?.segments[0].value, 1);
+            assert.equal(newPath?.segments[1].type, "rooms");
+            assert.deepEqual(newPath?.segments[1].value, ["", "b", "c"]);
+            assert.equal(newPath?.segments[2].type, "room");
+            assert.equal(newPath?.segments[2].value, "b");
         },
         "remove inactive room from grid path with empty tile": assert => {
-            const nav = new Navigation(allowsChild);
+            const nav: Navigation<SegmentType> = new Navigation(allowsChild);
             const path = nav.pathFrom([
                 new Segment("session", 1),
                 new Segment("rooms", ["a", "b", ""]),
                 new Segment("empty-grid-tile", 3)
             ]);
             const newPath = removeRoomFromPath(path, "b");
-            assert.equal(newPath.segments.length, 3);
-            assert.equal(newPath.segments[0].type, "session");
-            assert.equal(newPath.segments[0].value, 1);
-            assert.equal(newPath.segments[1].type, "rooms");
-            assert.deepEqual(newPath.segments[1].value, ["a", "", ""]);
-            assert.equal(newPath.segments[2].type, "empty-grid-tile");
-            assert.equal(newPath.segments[2].value, 3);
+            assert.equal(newPath?.segments.length, 3);
+            assert.equal(newPath?.segments[0].type, "session");
+            assert.equal(newPath?.segments[0].value, 1);
+            assert.equal(newPath?.segments[1].type, "rooms");
+            assert.deepEqual(newPath?.segments[1].value, ["a", "", ""]);
+            assert.equal(newPath?.segments[2].type, "empty-grid-tile");
+            assert.equal(newPath?.segments[2].value, 3);
         },
         "remove active room": assert => {
-            const nav = new Navigation(allowsChild);
+            const nav: Navigation<SegmentType> = new Navigation(allowsChild);
             const path = nav.pathFrom([
                 new Segment("session", 1),
                 new Segment("room", "b")
             ]);
             const newPath = removeRoomFromPath(path, "b");
-            assert.equal(newPath.segments.length, 1);
-            assert.equal(newPath.segments[0].type, "session");
-            assert.equal(newPath.segments[0].value, 1);
+            assert.equal(newPath?.segments.length, 1);
+            assert.equal(newPath?.segments[0].type, "session");
+            assert.equal(newPath?.segments[0].value, 1);
         },
         "remove inactive room doesn't do anything": assert => {
-            const nav = new Navigation(allowsChild);
+            const nav: Navigation<SegmentType> = new Navigation(allowsChild);
             const path = nav.pathFrom([
                 new Segment("session", 1),
                 new Segment("room", "b")
             ]);
             const newPath = removeRoomFromPath(path, "a");
-            assert.equal(newPath.segments.length, 2);
-            assert.equal(newPath.segments[0].type, "session");
-            assert.equal(newPath.segments[0].value, 1);
-            assert.equal(newPath.segments[1].type, "room");
-            assert.equal(newPath.segments[1].value, "b");
+            assert.equal(newPath?.segments.length, 2);
+            assert.equal(newPath?.segments[0].type, "session");
+            assert.equal(newPath?.segments[0].value, 1);
+            assert.equal(newPath?.segments[1].type, "room");
+            assert.equal(newPath?.segments[1].value, "b");
         },
         
     }
diff --git a/src/domain/session/RoomGridViewModel.js b/src/domain/session/RoomGridViewModel.js
index a7d19054..8e443e2d 100644
--- a/src/domain/session/RoomGridViewModel.js
+++ b/src/domain/session/RoomGridViewModel.js
@@ -15,7 +15,7 @@ limitations under the License.
 */
 
 import {ViewModel} from "../ViewModel";
-import {addPanelIfNeeded} from "../navigation/index.js";
+import {addPanelIfNeeded} from "../navigation/index";
 
 function dedupeSparse(roomIds) {
     return roomIds.map((id, idx) => {
@@ -185,7 +185,7 @@ export class RoomGridViewModel extends ViewModel {
     }
 }
 
-import {createNavigation} from "../navigation/index.js";
+import {createNavigation} from "../navigation/index";
 import {ObservableValue} from "../../observable/ObservableValue";
 
 export function tests() { 
diff --git a/src/domain/session/leftpanel/LeftPanelViewModel.js b/src/domain/session/leftpanel/LeftPanelViewModel.js
index 2fd3ca7e..8c8d71a2 100644
--- a/src/domain/session/leftpanel/LeftPanelViewModel.js
+++ b/src/domain/session/leftpanel/LeftPanelViewModel.js
@@ -21,7 +21,7 @@ import {InviteTileViewModel} from "./InviteTileViewModel.js";
 import {RoomBeingCreatedTileViewModel} from "./RoomBeingCreatedTileViewModel.js";
 import {RoomFilter} from "./RoomFilter.js";
 import {ApplyMap} from "../../../observable/map/ApplyMap.js";
-import {addPanelIfNeeded} from "../../navigation/index.js";
+import {addPanelIfNeeded} from "../../navigation/index";
 
 export class LeftPanelViewModel extends ViewModel {
     constructor(options) {
diff --git a/src/lib.ts b/src/lib.ts
index 90bf597c..4d1f906f 100644
--- a/src/lib.ts
+++ b/src/lib.ts
@@ -18,7 +18,7 @@ export {Platform} from "./platform/web/Platform.js";
 export {Client, LoadStatus} from "./matrix/Client.js";
 export {RoomStatus} from "./matrix/room/common";
 // export main view & view models
-export {createNavigation, createRouter} from "./domain/navigation/index.js";
+export {createNavigation, createRouter} from "./domain/navigation/index";
 export {RootViewModel} from "./domain/RootViewModel.js";
 export {RootView} from "./platform/web/ui/RootView.js";
 export {SessionViewModel} from "./domain/session/SessionViewModel.js";
diff --git a/src/platform/web/main.js b/src/platform/web/main.js
index edc2cf14..83644456 100644
--- a/src/platform/web/main.js
+++ b/src/platform/web/main.js
@@ -17,7 +17,7 @@ limitations under the License.
 
 // import {RecordRequester, ReplayRequester} from "./matrix/net/request/replay";
 import {RootViewModel} from "../../domain/RootViewModel.js";
-import {createNavigation, createRouter} from "../../domain/navigation/index.js";
+import {createNavigation, createRouter} from "../../domain/navigation/index";
 // Don't use a default export here, as we use multiple entries during legacy build,
 // which does not support default exports,
 // see https://github.com/rollup/plugins/tree/master/packages/multi-entry