Rewrite it in TypeScript; I have no idea if that works. It's still a work-in-progress.

src/widget/widget-prototype.ts

@@ -0,0 +1,33 @@
+/*
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+import WidgetCommonProperties = JQueryUI.WidgetCommonProperties;
+import {Uehrli} from "../uehrli";
+import {Options} from "./options";
+
+export interface WidgetPrototype extends WidgetCommonProperties {
+    options: Options;
+    start: () => void;
+    stop: () => void;
+    toggle: () => void;
+    language: (key: string) => void;
+    theme: (id: string) => void;
+    time: (time: Date) => void;
+    mode: (mode: string) => void;
+    width: (width: string) => void;
+    _create: () => void;
+    _destroy: () => void;
+    __fritteli_uhr_instance: Uehrli;
+}