diff --git a/src/domain/navigation/Navigation.ts b/src/domain/navigation/Navigation.ts
index b3b79a89..f0b29816 100644
--- a/src/domain/navigation/Navigation.ts
+++ b/src/domain/navigation/Navigation.ts
@@ -16,22 +16,6 @@ limitations under the License.
 
 import {BaseObservableValue, ObservableValue} from "../../observable/ObservableValue";
 
-type SegmentType = {
-    "login": true;
-    "session": string;
-    "sso": string;
-    "logout": true;
-    "room": string;
-    "rooms": string[];
-    "settings": true;
-    "create-room": true;
-    "empty-grid-tile": number;
-    "lightbox": string;
-    "right-panel": boolean;
-    "details": true;
-    "members": true;
-    "member": string;
-};
 
 type AllowsChild<T> = (parent: Segment<T> | undefined, child: Segment<T>) => boolean;
 
@@ -55,7 +39,7 @@ export class Navigation<T> {
         return this._path;
     }
 
-    push<K extends keyof T>(type: K, ...value: T[K] extends true? [undefined?]: [T[K]]): void {
+    push<K extends keyof T>(type: K, ...value: T[K] extends true? [(undefined | true)?]: [T[K]]): void {
         const newPath = this.path.with(new Segment(type, ...value));
         if (newPath) {
             this.applyPath(newPath);
@@ -107,7 +91,7 @@ export class Navigation<T> {
         return new Path(segments, this._allowsChild);
     }
 
-    segment<K extends keyof T>(type: K, ...value: T[K] extends true? [undefined?]: [T[K]]): Segment<T> {
+    segment<K extends keyof T>(type: K, ...value: T[K] extends true? [(undefined | true)?]: [T[K]]): Segment<T> {
         return new Segment(type, ...value);
     }
 }
@@ -133,7 +117,7 @@ function segmentValueEqual<T>(a?: T[keyof T], b?: T[keyof T]): boolean {
 export class Segment<T, K extends keyof T = any> {
     public value: T[K];
 
-    constructor(public type: K, ...value: T[K] extends true? [undefined?]: [T[K]]) {
+    constructor(public type: K, ...value: T[K] extends true? [(undefined | true)?]: [T[K]]) {
         this.value = (value[0] === undefined ? true : value[0]) as unknown as T[K];
     }
 }
@@ -231,6 +215,8 @@ class SegmentObservable<T> extends BaseObservableValue<T[keyof T] | undefined> {
     }
 }
 
+export type { Path };
+
 export function tests() {
 
     function createMockNavigation() {
diff --git a/src/domain/navigation/index.js b/src/domain/navigation/index.ts
similarity index 75%
rename from src/domain/navigation/index.js
rename to src/domain/navigation/index.ts
index 68fbe993..92cf41a1 100644
--- a/src/domain/navigation/index.js
+++ b/src/domain/navigation/index.ts
@@ -16,6 +16,24 @@ limitations under the License.
 
 import {Navigation, Segment} from "./Navigation";
 import {URLRouter} from "./URLRouter.js";
+import type { Path } from "./Navigation";
+
+type SegmentType = {
+    login: true;
+    session: string;
+    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() {
     return new Navigation(allowsChild);
@@ -25,7 +43,7 @@ export function createRouter({history, navigation}) {
     return new URLRouter({history, navigation, stringifyPath, parseUrlPath});
 }
 
-function allowsChild(parent, child) {
+function allowsChild(parent: {type: string, value: any} | undefined, child: {type: string, value: any}): 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> | null {
+    let newPath: Path<SegmentType> | null = 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 +106,29 @@ function roomsSegmentWithRoom(rooms, roomId, path) {
     }
 }
 
-function pushRightPanelSegment(array, segment, value = true) {
+// todo-self: verify code change here is okay
+function pushRightPanelSegment<T extends keyof SegmentType>(array: Segment<SegmentType>[], segment: T, ...value: SegmentType[T] extends true? [(undefined | true)?]: [SegmentType[T]]) {
     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) {
+export function parseUrlPath(urlPath: string, currentNavPath: Path<SegmentType>, defaultSessionId: string): Segment<SegmentType>[] {
     // substr(1) to take of initial /
     const parts = urlPath.substr(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 +190,9 @@ 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 +225,16 @@ 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 +244,7 @@ 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 +254,7 @@ 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 +266,15 @@ 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 +284,8 @@ 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 +295,8 @@ 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 +306,8 @@ 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");
@@ -285,13 +317,13 @@ 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"]),
                 new Segment("room", "b")
             ]);
-            const segments = parseUrlPath("/session/1/open-room/d", path);
+            const segments = parseUrlPath("/session/1/open-room/d", path, "");
             assert.equal(segments.length, 3);
             assert.equal(segments[0].type, "session");
             assert.equal(segments[0].value, "1");
@@ -301,13 +333,13 @@ 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"]),
                 new Segment("room", "b")
             ]);
-            const segments = parseUrlPath("/session/1/open-room/a", path);
+            const segments = parseUrlPath("/session/1/open-room/a", path, "");
             assert.equal(segments.length, 3);
             assert.equal(segments[0].type, "session");
             assert.equal(segments[0].value, "1");
@@ -317,7 +349,7 @@ 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"]),
@@ -325,7 +357,7 @@ export function tests() {
                 new Segment("right-panel", true),
                 new Segment("details", true)
             ]);
-            const segments = parseUrlPath("/session/1/open-room/a", path);
+            const segments = parseUrlPath("/session/1/open-room/a", path, "");
             assert.equal(segments.length, 5);
             assert.equal(segments[0].type, "session");
             assert.equal(segments[0].value, "1");
@@ -339,7 +371,7 @@ 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"]),
@@ -347,7 +379,7 @@ export function tests() {
                 new Segment("right-panel", true),
                 new Segment("members", true)
             ]);
-            const segments = parseUrlPath("/session/1/open-room/a/member/foo", path);
+            const segments = parseUrlPath("/session/1/open-room/a/member/foo", path, "");
             assert.equal(segments.length, 5);
             assert.equal(segments[0].type, "session");
             assert.equal(segments[0].value, "1");
@@ -361,13 +393,13 @@ 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"]),
                 new Segment("empty-grid-tile", 4)
             ]);
-            const segments = parseUrlPath("/session/1/open-room/d", path);
+            const segments = parseUrlPath("/session/1/open-room/d", path, "");
             assert.equal(segments.length, 3);
             assert.equal(segments[0].type, "session");
             assert.equal(segments[0].value, "1");
@@ -377,82 +409,83 @@ 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