diff --git a/src/domain/navigation/Navigation.js b/src/domain/navigation/Navigation.js
index 3167475f..340ae0d5 100644
--- a/src/domain/navigation/Navigation.js
+++ b/src/domain/navigation/Navigation.js
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {BaseObservableValue, ObservableValue} from "../../observable/ObservableValue.js";
+import {BaseObservableValue, ObservableValue} from "../../observable/ObservableValue";
 
 export class Navigation {
     constructor(allowsChild) {
diff --git a/src/domain/session/RoomGridViewModel.js b/src/domain/session/RoomGridViewModel.js
index 08887f3e..d89d821a 100644
--- a/src/domain/session/RoomGridViewModel.js
+++ b/src/domain/session/RoomGridViewModel.js
@@ -186,7 +186,7 @@ export class RoomGridViewModel extends ViewModel {
 }
 
 import {createNavigation} from "../navigation/index.js";
-import {ObservableValue} from "../../observable/ObservableValue.js";
+import {ObservableValue} from "../../observable/ObservableValue";
 
 export function tests() { 
     class RoomVMMock {
diff --git a/src/domain/session/RoomViewModelObservable.js b/src/domain/session/RoomViewModelObservable.js
index b9549905..2a706045 100644
--- a/src/domain/session/RoomViewModelObservable.js
+++ b/src/domain/session/RoomViewModelObservable.js
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {ObservableValue} from "../../observable/ObservableValue.js";
+import {ObservableValue} from "../../observable/ObservableValue";
 
 /**
 Depending on the status of a room (invited, joined, archived, or none),
@@ -77,4 +77,4 @@ export class RoomViewModelObservable extends ObservableValue {
         this.unsubscribeAll();
         this.get()?.dispose();
     }
-}
\ No newline at end of file
+}
diff --git a/src/domain/session/room/timeline/ReactionsViewModel.js b/src/domain/session/room/timeline/ReactionsViewModel.js
index ca5d43f0..25d74b49 100644
--- a/src/domain/session/room/timeline/ReactionsViewModel.js
+++ b/src/domain/session/room/timeline/ReactionsViewModel.js
@@ -189,7 +189,7 @@ import {HomeServer as MockHomeServer} from "../../../../mocks/HomeServer.js";
 // other imports
 import {BaseMessageTile} from "./tiles/BaseMessageTile.js";
 import {MappedList} from "../../../../observable/list/MappedList.js";
-import {ObservableValue} from "../../../../observable/ObservableValue.js";
+import {ObservableValue} from "../../../../observable/ObservableValue";
 import {PowerLevels} from "../../../../matrix/room/PowerLevels.js";
 
 export function tests() {
diff --git a/src/domain/session/room/timeline/TilesCollection.js b/src/domain/session/room/timeline/TilesCollection.js
index 497c0b0d..b3696fad 100644
--- a/src/domain/session/room/timeline/TilesCollection.js
+++ b/src/domain/session/room/timeline/TilesCollection.js
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {BaseObservableList} from "../../../../observable/list/BaseObservableList.js";
+import {BaseObservableList} from "../../../../observable/list/BaseObservableList";
 import {sortedIndex} from "../../../../utils/sortedIndex.js";
 
 // maps 1..n entries to 0..1 tile. Entries are what is stored in the timeline, either an event or fragmentboundary
diff --git a/src/matrix/Session.js b/src/matrix/Session.js
index 87a3150c..36c8e084 100644
--- a/src/matrix/Session.js
+++ b/src/matrix/Session.js
@@ -40,7 +40,7 @@ import {
     writeKey as ssssWriteKey,
 } from "./ssss/index.js";
 import {SecretStorage} from "./ssss/SecretStorage.js";
-import {ObservableValue, RetainedObservableValue} from "../observable/ObservableValue.js";
+import {ObservableValue, RetainedObservableValue} from "../observable/ObservableValue";
 
 const PICKLE_KEY = "DEFAULT_KEY";
 const PUSHER_KEY = "pusher";
diff --git a/src/matrix/SessionContainer.js b/src/matrix/SessionContainer.js
index 479bb7a8..899b07ed 100644
--- a/src/matrix/SessionContainer.js
+++ b/src/matrix/SessionContainer.js
@@ -18,7 +18,7 @@ limitations under the License.
 import {createEnum} from "../utils/enum.js";
 import {lookupHomeserver} from "./well-known.js";
 import {AbortableOperation} from "../utils/AbortableOperation";
-import {ObservableValue} from "../observable/ObservableValue.js";
+import {ObservableValue} from "../observable/ObservableValue";
 import {HomeServerApi} from "./net/HomeServerApi.js";
 import {Reconnector, ConnectionStatus} from "./net/Reconnector.js";
 import {ExponentialRetryDelay} from "./net/ExponentialRetryDelay.js";
diff --git a/src/matrix/Sync.js b/src/matrix/Sync.js
index bcd29ab4..e010f90d 100644
--- a/src/matrix/Sync.js
+++ b/src/matrix/Sync.js
@@ -15,7 +15,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {ObservableValue} from "../observable/ObservableValue.js";
+import {ObservableValue} from "../observable/ObservableValue";
 import {createEnum} from "../utils/enum.js";
 
 const INCREMENTAL_TIMEOUT = 30000;
diff --git a/src/matrix/net/Reconnector.js b/src/matrix/net/Reconnector.js
index d3cf790f..6fd2ca94 100644
--- a/src/matrix/net/Reconnector.js
+++ b/src/matrix/net/Reconnector.js
@@ -15,7 +15,7 @@ limitations under the License.
 */
 
 import {createEnum} from "../../utils/enum.js";
-import {ObservableValue} from "../../observable/ObservableValue.js";
+import {ObservableValue} from "../../observable/ObservableValue";
 
 export const ConnectionStatus = createEnum(
     "Waiting",
diff --git a/src/matrix/room/BaseRoom.js b/src/matrix/room/BaseRoom.js
index aac962ac..43b2cf51 100644
--- a/src/matrix/room/BaseRoom.js
+++ b/src/matrix/room/BaseRoom.js
@@ -29,7 +29,7 @@ import {ObservedEventMap} from "./ObservedEventMap.js";
 import {DecryptionSource} from "../e2ee/common.js";
 import {ensureLogItem} from "../../logging/utils.js";
 import {PowerLevels} from "./PowerLevels.js";
-import {RetainedObservableValue} from "../../observable/ObservableValue.js";
+import {RetainedObservableValue} from "../../observable/ObservableValue";
 
 const EVENT_ENCRYPTED_TYPE = "m.room.encrypted";
 
diff --git a/src/matrix/room/ObservedEventMap.js b/src/matrix/room/ObservedEventMap.js
index 59f0e26a..6b20f85e 100644
--- a/src/matrix/room/ObservedEventMap.js
+++ b/src/matrix/room/ObservedEventMap.js
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {BaseObservableValue} from "../../observable/ObservableValue.js";
+import {BaseObservableValue} from "../../observable/ObservableValue";
 
 export class ObservedEventMap {
     constructor(notifyEmpty) {
diff --git a/src/mocks/Clock.js b/src/mocks/Clock.js
index 97b7462a..440c4cb4 100644
--- a/src/mocks/Clock.js
+++ b/src/mocks/Clock.js
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {ObservableValue} from "../observable/ObservableValue.js";
+import {ObservableValue} from "../observable/ObservableValue";
 
 class Timeout {
     constructor(elapsed, ms) {
diff --git a/src/observable/BaseObservable.js b/src/observable/BaseObservable.ts
similarity index 76%
rename from src/observable/BaseObservable.js
rename to src/observable/BaseObservable.ts
index 0f9934c3..16bd3b81 100644
--- a/src/observable/BaseObservable.js
+++ b/src/observable/BaseObservable.ts
@@ -14,20 +14,18 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-export class BaseObservable {
-    constructor() {
-        this._handlers = new Set();
-    }
+export abstract class BaseObservable<T> {
+    protected _handlers: Set<T> = new Set<T>();
 
-    onSubscribeFirst() {
+    onSubscribeFirst(): void {
 
     }
 
-    onUnsubscribeLast() {
+    onUnsubscribeLast(): void {
 
     }
 
-    subscribe(handler) {
+    subscribe(handler: T): () => void {
         this._handlers.add(handler);
         if (this._handlers.size === 1) {
             this.onSubscribeFirst();
@@ -37,7 +35,7 @@ export class BaseObservable {
         };
     }
 
-    unsubscribe(handler) {
+    unsubscribe(handler: T | null): null {
         if (handler) {
             this._handlers.delete(handler);
             if (this._handlers.size === 0) {
@@ -48,14 +46,14 @@ export class BaseObservable {
         return null;
     }
 
-    unsubscribeAll() {
+    unsubscribeAll(): void {
         if (this._handlers.size !== 0) {
             this._handlers.clear();
             this.onUnsubscribeLast();
         }
     }
 
-    get hasSubscriptions() {
+    get hasSubscriptions(): boolean {
         return this._handlers.size !== 0;
     }
 
@@ -63,13 +61,11 @@ export class BaseObservable {
 }
 
 export function tests() {
-    class Collection extends BaseObservable {
-        constructor() {
-            super();
-            this.firstSubscribeCalls = 0;
-            this.firstUnsubscribeCalls = 0;
-        }
-        onSubscribeFirst() {  this.firstSubscribeCalls += 1; }
+    class Collection extends BaseObservable<{}> {
+        firstSubscribeCalls: number= 0;
+        firstUnsubscribeCalls: number = 0;
+
+        onSubscribeFirst() { this.firstSubscribeCalls += 1; }
         onUnsubscribeLast() { this.firstUnsubscribeCalls += 1; }
     }
 
diff --git a/src/observable/ObservableValue.js b/src/observable/ObservableValue.ts
similarity index 74%
rename from src/observable/ObservableValue.js
rename to src/observable/ObservableValue.ts
index 8a433444..02d5fc69 100644
--- a/src/observable/ObservableValue.js
+++ b/src/observable/ObservableValue.ts
@@ -15,21 +15,19 @@ limitations under the License.
 */
 
 import {AbortError} from "../utils/error.js";
-import {BaseObservable} from "./BaseObservable.js";
+import {BaseObservable} from "./BaseObservable";
 
 // like an EventEmitter, but doesn't have an event type
-export class BaseObservableValue extends BaseObservable {
-    emit(argument) {
+export abstract class BaseObservableValue<T> extends BaseObservable<(value: T) => void> {
+    emit(argument: T) {
         for (const h of this._handlers) {
             h(argument);
         }
     }
 
-    get() {
-        throw new Error("unimplemented");
-    }
+    abstract get(): T;
 
-    waitFor(predicate) {
+    waitFor(predicate: (value: T) => boolean): IWaitHandle<T> {
         if (predicate(this.get())) {
             return new ResolvedWaitForHandle(Promise.resolve(this.get()));
         } else {
@@ -38,8 +36,17 @@ export class BaseObservableValue extends BaseObservable {
     }
 }
 
-class WaitForHandle {
-    constructor(observable, predicate) {
+interface IWaitHandle<T> {
+    promise: Promise<T>;
+    dispose(): void;
+}
+
+class WaitForHandle<T> implements IWaitHandle<T> {
+    private _promise: Promise<T>
+    private _reject: ((reason?: any) => void) | null;
+    private _subscription: (() => void) | null;
+
+    constructor(observable: BaseObservableValue<T>, predicate: (value: T) => boolean) {
         this._promise = new Promise((resolve, reject) => {
             this._reject = reject;
             this._subscription = observable.subscribe(v => {
@@ -52,7 +59,7 @@ class WaitForHandle {
         });
     }
 
-    get promise() {
+    get promise(): Promise<T> {
         return this._promise;
     }
 
@@ -68,25 +75,24 @@ class WaitForHandle {
     }
 }
 
-class ResolvedWaitForHandle {
-    constructor(promise) {
-        this.promise = promise;
-    }
-
+class ResolvedWaitForHandle<T> implements IWaitHandle<T> {
+    constructor(public promise: Promise<T>) {}
     dispose() {}
 }
 
-export class ObservableValue extends BaseObservableValue {
-    constructor(initialValue) {
+export class ObservableValue<T> extends BaseObservableValue<T> {
+    private _value: T;
+
+    constructor(initialValue: T) {
         super();
         this._value = initialValue;
     }
 
-    get() {
+    get(): T {
         return this._value;
     }
 
-    set(value) {
+    set(value: T): void {
         if (value !== this._value) {
             this._value = value;
             this.emit(this._value);
@@ -94,8 +100,10 @@ export class ObservableValue extends BaseObservableValue {
     }
 }
 
-export class RetainedObservableValue extends ObservableValue {
-    constructor(initialValue, freeCallback) {
+export class RetainedObservableValue<T> extends ObservableValue<T> {
+    private _freeCallback: () => void;
+
+    constructor(initialValue: T, freeCallback: () => void) {
         super(initialValue);
         this._freeCallback = freeCallback;
     }
@@ -109,7 +117,7 @@ export class RetainedObservableValue extends ObservableValue {
 export function tests() {
     return {
         "set emits an update": assert => {
-            const a = new ObservableValue();
+            const a = new ObservableValue<number>(0);
             let fired = false;
             const subscription = a.subscribe(v => {
                 fired = true;
@@ -140,7 +148,7 @@ export function tests() {
             assert.strictEqual(a.get(), 6);
         },
         "waitFor promise rejects when disposed": async assert => {
-            const a = new ObservableValue();
+            const a = new ObservableValue<number>(0);
             const handle = a.waitFor(() => false);
             Promise.resolve().then(() => {
                 handle.dispose();
diff --git a/src/observable/list/AsyncMappedList.js b/src/observable/list/AsyncMappedList.js
index 604d8e94..9af1f95a 100644
--- a/src/observable/list/AsyncMappedList.js
+++ b/src/observable/list/AsyncMappedList.js
@@ -15,7 +15,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {BaseMappedList, runAdd, runUpdate, runRemove, runMove, runReset} from "./BaseMappedList.js";
+import {BaseMappedList, runAdd, runUpdate, runRemove, runMove, runReset} from "./BaseMappedList";
 
 export class AsyncMappedList extends BaseMappedList {
     constructor(sourceList, mapper, updater, removeCallback) {
diff --git a/src/observable/list/BaseMappedList.js b/src/observable/list/BaseMappedList.js
deleted file mode 100644
index 1ccd4e12..00000000
--- a/src/observable/list/BaseMappedList.js
+++ /dev/null
@@ -1,77 +0,0 @@
-/*
-Copyright 2020 Bruno Windels <bruno@windels.cloud>
-Copyright 2021 The Matrix.org Foundation C.I.C.
-
-Licensed under the Apache License, Version 2.0 (the "License");
-you may not use this file except in compliance with the License.
-You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-Unless required by applicable law or agreed to in writing, software
-distributed under the License is distributed on an "AS IS" BASIS,
-WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-See the License for the specific language governing permissions and
-limitations under the License.
-*/
-
-import {BaseObservableList} from "./BaseObservableList.js";
-import {findAndUpdateInArray} from "./common.js";
-
-export class BaseMappedList extends BaseObservableList {
-    constructor(sourceList, mapper, updater, removeCallback) {
-        super();
-        this._sourceList = sourceList;
-        this._mapper = mapper;
-        this._updater = updater;
-        this._removeCallback = removeCallback;
-        this._mappedValues = null;
-        this._sourceUnsubscribe = null;
-    }
-
-    findAndUpdate(predicate, updater) {
-        return findAndUpdateInArray(predicate, this._mappedValues, this, updater);
-    }
-
-    get length() {
-        return this._mappedValues.length;
-    }
-
-    [Symbol.iterator]() {
-        return this._mappedValues.values();
-    }
-}
-
-export function runAdd(list, index, mappedValue) {
-    list._mappedValues.splice(index, 0, mappedValue);
-    list.emitAdd(index, mappedValue);
-}
-
-export function runUpdate(list, index, value, params) {
-    const mappedValue = list._mappedValues[index];
-    if (list._updater) {
-        list._updater(mappedValue, params, value);
-    }
-    list.emitUpdate(index, mappedValue, params);
-}
-
-export function runRemove(list, index) {
-    const mappedValue = list._mappedValues[index];
-    list._mappedValues.splice(index, 1);
-    if (list._removeCallback) {
-        list._removeCallback(mappedValue);
-    }
-    list.emitRemove(index, mappedValue);
-}
-
-export function runMove(list, fromIdx, toIdx) {
-    const mappedValue = list._mappedValues[fromIdx];
-    list._mappedValues.splice(fromIdx, 1);
-    list._mappedValues.splice(toIdx, 0, mappedValue);
-    list.emitMove(fromIdx, toIdx, mappedValue);
-}
-
-export function runReset(list) {
-    list._mappedValues = [];
-    list.emitReset();
-}
diff --git a/src/observable/list/BaseMappedList.ts b/src/observable/list/BaseMappedList.ts
new file mode 100644
index 00000000..f339d113
--- /dev/null
+++ b/src/observable/list/BaseMappedList.ts
@@ -0,0 +1,85 @@
+/*
+Copyright 2020 Bruno Windels <bruno@windels.cloud>
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import {BaseObservableList} from "./BaseObservableList";
+import {findAndUpdateInArray} from "./common";
+
+export type Mapper<F,T> = (value: F) => T
+export type Updater<F,T> = (mappedValue: T, params: any, value: F) => void;
+
+export class BaseMappedList<F,T> extends BaseObservableList<T> {
+    protected _sourceList: BaseObservableList<F>;
+    protected _sourceUnsubscribe: (() => void) | null = null;
+    _mapper: Mapper<F,T>;
+    _updater: Updater<F,T>;
+    _removeCallback: ((value: T) => void) | null;
+    _mappedValues: T[] | null = null;
+
+    constructor(sourceList: BaseObservableList<F>, mapper: Mapper<F,T>, updater: Updater<F,T>, removeCallback: ((value: T) => void) | null = null) {
+        super();
+        this._sourceList = sourceList;
+        this._mapper = mapper;
+        this._updater = updater;
+        this._removeCallback = removeCallback;
+    }
+
+    findAndUpdate(predicate: (value: T) => boolean, updater: (value: T) => any | false) {
+        return findAndUpdateInArray(predicate, this._mappedValues!, this, updater);
+    }
+
+    get length() {
+        return this._mappedValues!.length;
+    }
+
+    [Symbol.iterator]() {
+        return this._mappedValues!.values();
+    }
+}
+
+export function runAdd<F,T>(list: BaseMappedList<F,T>, index: number, mappedValue: T): void {
+    list._mappedValues!.splice(index, 0, mappedValue);
+    list.emitAdd(index, mappedValue);
+}
+
+export function runUpdate<F,T>(list: BaseMappedList<F,T>, index: number, value: F, params: any): void {
+    const mappedValue = list._mappedValues![index];
+    if (list._updater) {
+        list._updater(mappedValue, params, value);
+    }
+    list.emitUpdate(index, mappedValue, params);
+}
+
+export function runRemove<F,T>(list: BaseMappedList<F,T>, index: number): void {
+    const mappedValue = list._mappedValues![index];
+    list._mappedValues!.splice(index, 1);
+    if (list._removeCallback) {
+        list._removeCallback(mappedValue);
+    }
+    list.emitRemove(index, mappedValue);
+}
+
+export function runMove<F,T>(list: BaseMappedList<F,T>, fromIdx: number, toIdx: number): void {
+    const mappedValue = list._mappedValues![fromIdx];
+    list._mappedValues!.splice(fromIdx, 1);
+    list._mappedValues!.splice(toIdx, 0, mappedValue);
+    list.emitMove(fromIdx, toIdx, mappedValue);
+}
+
+export function runReset<F,T>(list: BaseMappedList<F,T>): void {
+    list._mappedValues = [];
+    list.emitReset();
+}
diff --git a/src/observable/list/BaseObservableList.js b/src/observable/list/BaseObservableList.ts
similarity index 60%
rename from src/observable/list/BaseObservableList.js
rename to src/observable/list/BaseObservableList.ts
index b3757a13..9ba6559a 100644
--- a/src/observable/list/BaseObservableList.js
+++ b/src/observable/list/BaseObservableList.ts
@@ -14,9 +14,17 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {BaseObservable} from "../BaseObservable.js";
+import {BaseObservable} from "../BaseObservable";
 
-export class BaseObservableList extends BaseObservable {
+export interface IListObserver<T> {
+    onReset(list: BaseObservableList<T>): void;
+    onAdd(index: number, value:T, list: BaseObservableList<T>): void;
+    onUpdate(index: number, value: T, params: any, list: BaseObservableList<T>): void;
+    onRemove(index: number, value: T, list: BaseObservableList<T>): void
+    onMove(from: number, to: number, value: T, list: BaseObservableList<T>): void
+}
+
+export abstract class BaseObservableList<T> extends BaseObservable<IListObserver<T>> {
     emitReset() {
         for(let h of this._handlers) {
             h.onReset(this);
@@ -24,19 +32,19 @@ export class BaseObservableList extends BaseObservable {
     }
     // we need batch events, mostly on index based collection though?
     // maybe we should get started without?
-    emitAdd(index, value) {
+    emitAdd(index: number, value: T): void {
         for(let h of this._handlers) {
             h.onAdd(index, value, this);
         }
     }
 
-    emitUpdate(index, value, params) {
+    emitUpdate(index: number, value: T, params: any): void {
         for(let h of this._handlers) {
             h.onUpdate(index, value, params, this);
         }
     }
 
-    emitRemove(index, value) {
+    emitRemove(index: number, value: T): void {
         for(let h of this._handlers) {
             h.onRemove(index, value, this);
         }
@@ -44,17 +52,12 @@ export class BaseObservableList extends BaseObservable {
 
     // toIdx assumes the item has already
     // been removed from its fromIdx
-    emitMove(fromIdx, toIdx, value) {
+    emitMove(fromIdx: number, toIdx: number, value: T): void {
         for(let h of this._handlers) {
             h.onMove(fromIdx, toIdx, value, this);
         }
     }
 
-    [Symbol.iterator]() {
-        throw new Error("unimplemented");
-    }
-
-    get length() {
-        throw new Error("unimplemented");
-    }
+    abstract [Symbol.iterator](): IterableIterator<T>;
+    abstract get length(): number;
 }
diff --git a/src/observable/list/ConcatList.js b/src/observable/list/ConcatList.js
index d395e807..e87ccb60 100644
--- a/src/observable/list/ConcatList.js
+++ b/src/observable/list/ConcatList.js
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {BaseObservableList} from "./BaseObservableList.js";
+import {BaseObservableList} from "./BaseObservableList";
 
 export class ConcatList extends BaseObservableList {
     constructor(...sourceLists) {
diff --git a/src/observable/list/MappedList.js b/src/observable/list/MappedList.js
index 096a018f..c799fcff 100644
--- a/src/observable/list/MappedList.js
+++ b/src/observable/list/MappedList.js
@@ -15,7 +15,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {BaseMappedList, runAdd, runUpdate, runRemove, runMove, runReset} from "./BaseMappedList.js";
+import {BaseMappedList, runAdd, runUpdate, runRemove, runMove, runReset} from "./BaseMappedList";
 
 export class MappedList extends BaseMappedList {
     onSubscribeFirst() {
@@ -57,7 +57,7 @@ export class MappedList extends BaseMappedList {
 }
 
 import {ObservableArray} from "./ObservableArray.js";
-import {BaseObservableList} from "./BaseObservableList.js";
+import {BaseObservableList} from "./BaseObservableList";
 
 export async function tests() {
     class MockList extends BaseObservableList {
diff --git a/src/observable/list/ObservableArray.js b/src/observable/list/ObservableArray.js
index 0f9ee99d..5d9f5c12 100644
--- a/src/observable/list/ObservableArray.js
+++ b/src/observable/list/ObservableArray.js
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {BaseObservableList} from "./BaseObservableList.js";
+import {BaseObservableList} from "./BaseObservableList";
 
 export class ObservableArray extends BaseObservableList {
     constructor(initialValues = []) {
diff --git a/src/observable/list/SortedArray.js b/src/observable/list/SortedArray.js
index 323cf776..874d1b04 100644
--- a/src/observable/list/SortedArray.js
+++ b/src/observable/list/SortedArray.js
@@ -14,9 +14,9 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {BaseObservableList} from "./BaseObservableList.js";
+import {BaseObservableList} from "./BaseObservableList";
 import {sortedIndex} from "../../utils/sortedIndex.js";
-import {findAndUpdateInArray} from "./common.js";
+import {findAndUpdateInArray} from "./common";
 
 export class SortedArray extends BaseObservableList {
     constructor(comparator) {
diff --git a/src/observable/list/SortedMapList.js b/src/observable/list/SortedMapList.js
index babf5c35..2421419e 100644
--- a/src/observable/list/SortedMapList.js
+++ b/src/observable/list/SortedMapList.js
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {BaseObservableList} from "./BaseObservableList.js";
+import {BaseObservableList} from "./BaseObservableList";
 import {sortedIndex} from "../../utils/sortedIndex.js";
 
 /*
diff --git a/src/observable/list/common.js b/src/observable/list/common.ts
similarity index 83%
rename from src/observable/list/common.js
rename to src/observable/list/common.ts
index 8dbf7873..c67a841b 100644
--- a/src/observable/list/common.js
+++ b/src/observable/list/common.ts
@@ -14,9 +14,10 @@ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 */
+import {BaseObservableList} from "./BaseObservableList";
 
 /* inline update of item in collection backed by array, without replacing the preexising item */
-export function findAndUpdateInArray(predicate, array, observable, updater) {
+export function findAndUpdateInArray<T>(predicate: (value: T) => boolean, array: T[], observable: BaseObservableList<T>, updater: (value: T) => any | false) {
     const index = array.findIndex(predicate);
     if (index !== -1) {
         const value = array[index];
@@ -29,4 +30,4 @@ export function findAndUpdateInArray(predicate, array, observable, updater) {
         return true;
     }
     return false;
-}
\ No newline at end of file
+}
diff --git a/src/observable/map/BaseObservableMap.js b/src/observable/map/BaseObservableMap.js
index 79df21f6..d3193931 100644
--- a/src/observable/map/BaseObservableMap.js
+++ b/src/observable/map/BaseObservableMap.js
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {BaseObservable} from "../BaseObservable.js";
+import {BaseObservable} from "../BaseObservable";
 
 export class BaseObservableMap extends BaseObservable {
     emitReset() {
diff --git a/src/platform/web/dom/History.js b/src/platform/web/dom/History.js
index 68e4ef78..d51974bb 100644
--- a/src/platform/web/dom/History.js
+++ b/src/platform/web/dom/History.js
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {BaseObservableValue} from "../../../observable/ObservableValue.js";
+import {BaseObservableValue} from "../../../observable/ObservableValue";
 
 export class History extends BaseObservableValue {
     handleEvent(event) {
diff --git a/src/platform/web/dom/OnlineStatus.js b/src/platform/web/dom/OnlineStatus.js
index 588c0815..48e4e912 100644
--- a/src/platform/web/dom/OnlineStatus.js
+++ b/src/platform/web/dom/OnlineStatus.js
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {BaseObservableValue} from "../../../observable/ObservableValue.js";
+import {BaseObservableValue} from "../../../observable/ObservableValue";
 
 export class OnlineStatus extends BaseObservableValue {
     constructor() {
diff --git a/src/platform/web/ui/general/ListView.ts b/src/platform/web/ui/general/ListView.ts
index cdfdbf76..e6d15755 100644
--- a/src/platform/web/ui/general/ListView.ts
+++ b/src/platform/web/ui/general/ListView.ts
@@ -16,7 +16,7 @@ limitations under the License.
 
 import {el} from "./html";
 import {mountView, insertAt} from "./utils";
-import {BaseObservableList as ObservableList} from "../../../../observable/list/BaseObservableList.js";
+import {BaseObservableList as ObservableList} from "../../../../observable/list/BaseObservableList";
 import {IView, IMountArgs} from "./types";
 
 interface IOptions<T, V> {
@@ -27,7 +27,7 @@ interface IOptions<T, V> {
     parentProvidesUpdates?: boolean
 }
 
-type SubscriptionHandle = () => undefined;
+type SubscriptionHandle = () => void;
 
 export class ListView<T, V extends IView> implements IView {
 
@@ -115,7 +115,8 @@ export class ListView<T, V extends IView> implements IView {
     }
 
     private _unloadList() {
-        this._subscription = this._subscription!();
+        this._subscription!()
+        this._subscription = undefined;
         for (let child of this._childInstances!) {
             child.unmount();
         }
@@ -137,26 +138,34 @@ export class ListView<T, V extends IView> implements IView {
         this._root!.appendChild(fragment);
     }
 
-    protected onAdd(idx: number, value: T) {
+    onReset() {
+        for (const child of this._childInstances!) {
+            child.root()!.remove();
+            child.unmount();
+        }
+        this._childInstances!.length = 0;
+    }
+
+    onAdd(idx: number, value: T) {
         const child = this._childCreator(value);
         this._childInstances!.splice(idx, 0, child);
         insertAt(this._root!, idx, mountView(child, this._mountArgs));
     }
 
-    protected onRemove(idx: number, value: T) {
+    onRemove(idx: number, value: T) {
         const [child] = this._childInstances!.splice(idx, 1);
         child.root()!.remove();
         child.unmount();
     }
 
-    protected onMove(fromIdx: number, toIdx: number, value: T) {
+    onMove(fromIdx: number, toIdx: number, value: T) {
         const [child] = this._childInstances!.splice(fromIdx, 1);
         this._childInstances!.splice(toIdx, 0, child);
         child.root()!.remove();
         insertAt(this._root!, toIdx, child.root()! as Element);
     }
 
-    protected onUpdate(i: number, value: T, params: any) {
+    onUpdate(i: number, value: T, params: any) {
         if (this._childInstances) {
             const instance = this._childInstances![i];
             instance && instance.update(value, params);
diff --git a/src/platform/web/ui/session/room/TimelineView.ts b/src/platform/web/ui/session/room/TimelineView.ts
index a4e143aa..da3dc537 100644
--- a/src/platform/web/ui/session/room/TimelineView.ts
+++ b/src/platform/web/ui/session/room/TimelineView.ts
@@ -26,7 +26,7 @@ import {MissingAttachmentView} from "./timeline/MissingAttachmentView.js";
 import {AnnouncementView} from "./timeline/AnnouncementView.js";
 import {RedactedView} from "./timeline/RedactedView.js";
 import {SimpleTile} from "../../../../../domain/session/room/timeline/tiles/SimpleTile.js";
-import {BaseObservableList as ObservableList} from "../../../../../observable/list/BaseObservableList.js";
+import {BaseObservableList as ObservableList} from "../../../../../observable/list/BaseObservableList";
 
 //import {TimelineViewModel} from "../../../../../domain/session/room/timeline/TimelineViewModel.js";
 export interface TimelineViewModel extends IObservableValue {
@@ -211,7 +211,12 @@ class TilesListView extends ListView<SimpleTile, TileView> {
         this.onChanged = onChanged;
     }
 
-    protected onUpdate(index: number, value: SimpleTile, param: any) {
+    onReset() {
+        super.onReset();
+        this.onChanged();
+    }
+
+    onUpdate(index: number, value: SimpleTile, param: any) {
         if (param === "shape") {
             const ExpectedClass = viewClassForEntry(value);
             const child = this.getChildInstanceByIndex(index);
@@ -227,17 +232,17 @@ class TilesListView extends ListView<SimpleTile, TileView> {
         this.onChanged();
     }
 
-    protected onAdd(idx: number, value: SimpleTile) {
+    onAdd(idx: number, value: SimpleTile) {
         super.onAdd(idx, value);
         this.onChanged();
     }
 
-    protected onRemove(idx: number, value: SimpleTile) {
+    onRemove(idx: number, value: SimpleTile) {
         super.onRemove(idx, value);
         this.onChanged();
     }
 
-    protected onMove(fromIdx: number, toIdx: number, value: SimpleTile) {
+    onMove(fromIdx: number, toIdx: number, value: SimpleTile) {
         super.onMove(fromIdx, toIdx, value);
         this.onChanged();
     }