diff --git a/src/matrix/room/timeline/entries/BaseEntry.js b/src/matrix/room/timeline/entries/BaseEntry.ts
similarity index 80%
rename from src/matrix/room/timeline/entries/BaseEntry.js
rename to src/matrix/room/timeline/entries/BaseEntry.ts
index ae3ddf05..c592ecb6 100644
--- a/src/matrix/room/timeline/entries/BaseEntry.js
+++ b/src/matrix/room/timeline/entries/BaseEntry.ts
@@ -18,20 +18,26 @@ limitations under the License.
 import {EventKey} from "../EventKey.js";
 export const PENDING_FRAGMENT_ID = Number.MAX_SAFE_INTEGER;
 
+interface FragmentIdComparer {
+    compare: (a: number, b: number) => number
+}
+
 export class BaseEntry {
-    constructor(fragmentIdComparer) {
+    protected _fragmentIdComparer: FragmentIdComparer
+
+    constructor(fragmentIdComparer: FragmentIdComparer) {
         this._fragmentIdComparer = fragmentIdComparer;
     }
 
-    get fragmentId() {
+    get fragmentId(): number {
         throw new Error("unimplemented");
     }
 
-    get entryIndex() {
+    get entryIndex(): number {
         throw new Error("unimplemented");
     }
 
-    compare(otherEntry) {
+    compare(otherEntry: BaseEntry): number {
         if (this.fragmentId === otherEntry.fragmentId) {
             return this.entryIndex - otherEntry.entryIndex;
         } else if (this.fragmentId === PENDING_FRAGMENT_ID) {
@@ -44,9 +50,9 @@ export class BaseEntry {
         }
     }
 
-    asEventKey() {
+    asEventKey(): EventKey {
         return new EventKey(this.fragmentId, this.entryIndex);
     }
 
-    updateFrom() {}
+    updateFrom(other: BaseEntry) {}
 }
diff --git a/src/matrix/room/timeline/entries/BaseEventEntry.js b/src/matrix/room/timeline/entries/BaseEventEntry.js
index 2e681104..7eb0fc94 100644
--- a/src/matrix/room/timeline/entries/BaseEventEntry.js
+++ b/src/matrix/room/timeline/entries/BaseEventEntry.js
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {BaseEntry} from "./BaseEntry.js";
+import {BaseEntry} from "./BaseEntry";
 import {REDACTION_TYPE} from "../../common.js";
 import {createAnnotation, ANNOTATION_RELATION_TYPE, getRelationFromContent} from "../relations.js";
 import {PendingAnnotation} from "../PendingAnnotation.js";
diff --git a/src/matrix/room/timeline/entries/FragmentBoundaryEntry.js b/src/matrix/room/timeline/entries/FragmentBoundaryEntry.js
index 0eb2a5b6..3d4bd67b 100644
--- a/src/matrix/room/timeline/entries/FragmentBoundaryEntry.js
+++ b/src/matrix/room/timeline/entries/FragmentBoundaryEntry.js
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {BaseEntry} from "./BaseEntry.js";
+import {BaseEntry} from "./BaseEntry";
 import {Direction} from "../Direction.js";
 import {isValidFragmentId} from "../common.js";
 import {KeyLimits} from "../../../storage/common.js";
diff --git a/src/matrix/room/timeline/entries/PendingEventEntry.js b/src/matrix/room/timeline/entries/PendingEventEntry.js
index 742bff49..4bc3c47e 100644
--- a/src/matrix/room/timeline/entries/PendingEventEntry.js
+++ b/src/matrix/room/timeline/entries/PendingEventEntry.js
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {PENDING_FRAGMENT_ID} from "./BaseEntry.js";
+import {PENDING_FRAGMENT_ID} from "./BaseEntry";
 import {BaseEventEntry} from "./BaseEventEntry.js";
 
 export class PendingEventEntry extends BaseEventEntry {