add documentation how to listen to view_closed events slackapi#1010

docs/_basic/listening_modals.md

@@ -1,21 +1,23 @@
 ---
-title: Listening for view submissions
+title: Listening for view changes
 lang: en
 slug: view-submissions
 order: 12
 ---
 
 <div class="section-content">
-If a <a href="https://api.slack.com/reference/block-kit/views">view payload</a> contains any input blocks, you must listen to `view_submission` requests to receive their values. To listen to `view_submission` requests, you can use the built-in `view()` method.
 
-`view()` requires a `callback_id` of type `string` or `RegExp`.
+If a <a href="https://api.slack.com/reference/block-kit/views">view payload</a> contains any input blocks, you must listen to `view_submission` requests to receive their values.
+If the `notify_on_close` flag of a view is active, an respective event is sent when a view has been closed.
+To listen to either a `view_submission` request or `view_closed` event, you can use the built-in `view()` method.
 
-You can access the value of the input blocks by accessing the `state` object. `state` contains a values object that uses the `block_id` and unique `action_id` to store the input values.
+`view()` requires a `callback_id` of type `string` or `RegExp` or a constraint object with properties `type` and `callback_id`. 
 
 ---
 
 ##### Update views on submission
 
+You can access the value of the input blocks by accessing the `state` object. `state` contains a values object that uses the `block_id` and unique `action_id` to store the input values.
 To update a view in response to a `view_submission` request, you may pass a `response_action` of type `update` with a newly composed `view` to display in your acknowledgement.
 
 ```javascript
@@ -69,3 +71,23 @@ app.view('view_b', async ({ ack, body, view, client }) => {
 
 });
 ```
+
+---
+
+##### handle view closed events
+
+The built-in `view()` method can also handle `view_closed` events, which are sent when a <a href="https://api.slack.com/reference/block-kit/views">view payload</a> has the `notify_on_close` flag set.
+The event contains the respective `callback_id` of the closed view.
+Please note that you have to specify the `type: 'view_closed'` in the constraint object explicitly, since otherwise the handler is not triggered.
+
+See the <a href="https://api.slack.com/surfaces/modals/using#modal_cancellations">API documentation</a> for more information about the view closed event.
+
+```javascript
+// Handle a view_canceled event
+app.view({ type: 'view_closed', callback_id: 'view_b' }, async ({ ack, body, view, client }) => {
+  // Acknowledge the view_closed event
+  await ack();
+
+  // react on close event
+});
+```