diff --git a/src/matrix/SessionContainer.js b/src/matrix/SessionContainer.js
index 44d7b3e4..89325d49 100644
--- a/src/matrix/SessionContainer.js
+++ b/src/matrix/SessionContainer.js
@@ -21,7 +21,7 @@ import {AbortableOperation} from "../utils/AbortableOperation";
 import {ObservableValue} from "../observable/ObservableValue";
 import {HomeServerApi} from "./net/HomeServerApi.js";
 import {Reconnector, ConnectionStatus} from "./net/Reconnector.js";
-import {ExponentialRetryDelay} from "./net/ExponentialRetryDelay.js";
+import {ExponentialRetryDelay} from "./net/ExponentialRetryDelay";
 import {MediaRepository} from "./net/MediaRepository.js";
 import {RequestScheduler} from "./net/RequestScheduler.js";
 import {Sync, SyncStatus} from "./Sync.js";
diff --git a/src/matrix/net/ExponentialRetryDelay.js b/src/matrix/net/ExponentialRetryDelay.ts
similarity index 86%
rename from src/matrix/net/ExponentialRetryDelay.js
rename to src/matrix/net/ExponentialRetryDelay.ts
index 853f8758..a6a874f3 100644
--- a/src/matrix/net/ExponentialRetryDelay.js
+++ b/src/matrix/net/ExponentialRetryDelay.ts
@@ -15,18 +15,28 @@ limitations under the License.
 */
 
 import {AbortError} from "../../utils/error";
+import type {Timeout} from "../../platform/web/dom/Clock.js";
+
+type TimeoutCreator = (ms: number) => Timeout;
+
+const enum Default { start = 2000 }
 
 export class ExponentialRetryDelay {
-    constructor(createTimeout) {
+    private readonly _start: number = Default.start;
+    private _current: number = Default.start;
+    private readonly _createTimeout: TimeoutCreator;
+    private readonly _max: number;
+    private _timeout?: Timeout;
+
+    constructor(createTimeout: TimeoutCreator) {
         const start = 2000;
         this._start = start;
         this._current = start;
         this._createTimeout = createTimeout;
         this._max = 60 * 5 * 1000; //5 min
-        this._timeout = null;
     }
 
-    async waitForRetry() {
+    async waitForRetry(): Promise<void> {
         this._timeout = this._createTimeout(this._current);
         try {
             await this._timeout.elapsed();
@@ -39,22 +49,22 @@ export class ExponentialRetryDelay {
                 throw err;
             }
         } finally {
-            this._timeout = null;
+            this._timeout = undefined;
         }
     }
 
-    abort() {
+    abort(): void {
         if (this._timeout) {
             this._timeout.abort();
         }
     }
 
-    reset() {
+    reset(): void {
         this._current = this._start;
         this.abort();
     }
 
-    get nextValue() {
+    get nextValue(): number {
         return this._current;
     }
 }
diff --git a/src/matrix/net/HomeServerApi.js b/src/matrix/net/HomeServerApi.js
index 308e71d9..01f5cb45 100644
--- a/src/matrix/net/HomeServerApi.js
+++ b/src/matrix/net/HomeServerApi.js
@@ -15,7 +15,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {encodeQueryParams, encodeBody} from "./common.js";
+import {encodeQueryParams, encodeBody} from "./common";
 import {HomeServerRequest} from "./HomeServerRequest.js";
 
 const CS_R0_PREFIX = "/_matrix/client/r0";
diff --git a/src/matrix/net/MediaRepository.js b/src/matrix/net/MediaRepository.js
index 3f718c85..a7875d99 100644
--- a/src/matrix/net/MediaRepository.js
+++ b/src/matrix/net/MediaRepository.js
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {encodeQueryParams} from "./common.js";
+import {encodeQueryParams} from "./common";
 import {decryptAttachment} from "../e2ee/attachment.js";
 
 export class MediaRepository {
diff --git a/src/matrix/net/Reconnector.js b/src/matrix/net/Reconnector.js
index 6eaa78d7..c4231c79 100644
--- a/src/matrix/net/Reconnector.js
+++ b/src/matrix/net/Reconnector.js
@@ -120,7 +120,7 @@ export class Reconnector {
 
 
 import {Clock as MockClock} from "../../mocks/Clock.js";
-import {ExponentialRetryDelay} from "./ExponentialRetryDelay.js";
+import {ExponentialRetryDelay} from "./ExponentialRetryDelay";
 import {ConnectionError} from "../error.js"
 
 export function tests() {
diff --git a/src/matrix/net/RequestScheduler.js b/src/matrix/net/RequestScheduler.js
index f9adec97..b5c5a8fc 100644
--- a/src/matrix/net/RequestScheduler.js
+++ b/src/matrix/net/RequestScheduler.js
@@ -18,7 +18,7 @@ limitations under the License.
 import {AbortError} from "../../utils/error";
 import {HomeServerError} from "../error.js";
 import {HomeServerApi} from "./HomeServerApi.js";
-import {ExponentialRetryDelay} from "./ExponentialRetryDelay.js";
+import {ExponentialRetryDelay} from "./ExponentialRetryDelay";
 
 class Request {
     constructor(methodName, args) {
diff --git a/src/platform/types/Platform.ts b/src/platform/types/Platform.ts
index 1cc972a8..b8b715ed 100644
--- a/src/platform/types/Platform.ts
+++ b/src/platform/types/Platform.ts
@@ -14,6 +14,8 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+// todo: this file should be called something else?
+
 import type {RequestResult} from "../web/dom/request/fetch.js";
 import type {IEncodedBody} from "../../matrix/net/common";