diff --git a/src/observable/BaseObservable.js b/src/observable/BaseObservable.ts
similarity index 100%
rename from src/observable/BaseObservable.js
rename to src/observable/BaseObservable.ts
diff --git a/src/observable/ObservableValue.js b/src/observable/ObservableValue.js
index 8a433444..00e3f021 100644
--- a/src/observable/ObservableValue.js
+++ b/src/observable/ObservableValue.js
@@ -15,7 +15,7 @@ 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 {
diff --git a/src/observable/list/BaseObservableList.js b/src/observable/list/BaseObservableList.js
index b3757a13..e2d8c3d5 100644
--- a/src/observable/list/BaseObservableList.js
+++ b/src/observable/list/BaseObservableList.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 BaseObservableList extends BaseObservable {
     emitReset() {
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() {