fix(panel): return value from dispose (#3895)

Author: samouss

src/widgets/panel/__tests__/panel-test.js

@@ -182,4 +182,19 @@ describe('Lifecycle', () => {
     expect(widget.render).toHaveBeenCalledTimes(1);
     expect(widget.dispose).toHaveBeenCalledTimes(1);
   });
+
+  test('returns the `state` from the widget dispose function', () => {
+    const widget = {
+      dispose: jest.fn(() => 'nextState'),
+    };
+    const widgetFactory = () => widget;
+
+    const widgetWithPanel = panel()(widgetFactory)({
+      container: document.createElement('div'),
+    });
+
+    const nextState = widgetWithPanel.dispose({});
+
+    expect(nextState).toBe('nextState');
+  });
 });

src/widgets/panel/panel.js

@@ -179,8 +179,10 @@ export default function panel({
         unmountComponentAtNode(getContainerNode(container));
 
         if (typeof widget.dispose === 'function') {
-          widget.dispose.call(this, ...args);
+          return widget.dispose.call(this, ...args);
         }
+
+        return undefined;
       },
       render(...args) {
         const [options] = args;