fix: stopped onChange throwing undefined (#18452)

* fix: restricted onchange calls

* fix: added new story and reverted default story

* test: added tests to check for undefined

* test removal

* chore: format fix

packages/react/src/components/ComboBox/ComboBox-test.js

@@ -621,6 +621,40 @@ describe('ComboBox', () => {
         'cds--list-box__menu-item--highlighted'
       );
     });
+
+    it('should pass defined selectedItem to onChange when item is selected', async () => {
+      render(<ComboBox {...mockProps} />);
+
+      expect(mockProps.onChange).not.toHaveBeenCalled();
+
+      await openMenu();
+      await userEvent.click(screen.getAllByRole('option')[0]);
+
+      expect(mockProps.onChange).toHaveBeenCalledTimes(1);
+      expect(mockProps.onChange).toHaveBeenCalledWith(
+        expect.objectContaining({
+          selectedItem: expect.anything(),
+        })
+      );
+
+      const call = mockProps.onChange.mock.calls[0][0];
+      expect(call.selectedItem).toBeDefined();
+      expect(call.selectedItem).toEqual(mockProps.items[0]);
+    });
+
+    it('should never pass undefined as selectedItem to onChange', async () => {
+      render(<ComboBox {...mockProps} />);
+
+      for (let i = 0; i < mockProps.items.length; i++) {
+        await openMenu();
+        await userEvent.click(screen.getAllByRole('option')[i]);
+
+        const call = mockProps.onChange.mock.calls[i][0];
+        expect(call.selectedItem).toBeDefined();
+        expect(call.selectedItem).not.toBeUndefined();
+        expect(call.selectedItem).toEqual(mockProps.items[i]);
+      }
+    });
   });
 
   describe('ComboBox autocomplete', () => {

packages/react/src/components/ComboBox/ComboBox.tsx

@@ -783,8 +783,9 @@ const ComboBox = forwardRef(
           onChange({ selectedItem: newSelectedItem });
         }
         if (
-          type === useCombobox.stateChangeTypes.FunctionSelectItem ||
-          type === useCombobox.stateChangeTypes.InputKeyDownEnter
+          (type === useCombobox.stateChangeTypes.FunctionSelectItem ||
+            type === useCombobox.stateChangeTypes.InputKeyDownEnter) &&
+          !isEqual(selectedItemProp, newSelectedItem) // Only fire if there's an actual change
         ) {
           onChange({ selectedItem: newSelectedItem });
         }