Closing an #ajax dialog triggers Javascript errors when scrolling

Right so you shouldn't use the X. It was removed at one point because we had problems making detachBehaviors run upon closing. The error you're seeing basically.

Shouldn't it work this way? Drupal.dialog is a bit mess

Look into this issue again.

+++ b/core/misc/dialog/dialog.js
@@ -31,6 +31,7 @@
     close: function (event) {
+      Drupal.dialog(event.target).close();
       Drupal.detachBehaviors(event.target, null, 'unload');

have to make sure `close` method in Drupal.dialog to be called.

I use patch from @droplet and it's OK now.

This same error occurs related to editing content with the core WYSIWYG.

1. Click to add a basic page.
2. Click the image icon in the WYSIWYG. A dialog pops up.
3. Close the dialog, using the top right X button.
4. Scroll in the page.
5. See your browser Javascript console.

the patch should be fixed it globally, please test :)

There is any actual point in moving all that code to the start of Drupal.dialog?

var hoisting, more closing to Drupal JS Code Standard.

+++ b/core/misc/dialog/dialog.js
@@ -60,6 +61,18 @@
+      returnValue: null,

actually it has one line change from `undef` to `null`

I applied the patch and it fixes the issue when scrolling.

I've confirmed that the patch fixes the bug but...

+++ b/core/misc/dialog/dialog.js
@@ -60,6 +61,18 @@
+      returnValue: null,

@@ -78,20 +91,6 @@
-    var undef;
...
-      returnValue: undef,

This is an API change. We shouldn't be making unnecessary API changes in bug fixes. Even if the current API is against our coding standards.

Changed as per #15

@tic2000 thanks for making the changes - really someone else should come in and rtbc them. People can and do disagree with me :)

Good to go.

Committed 393d5b1 and pushed to 8.0.x and 8.1.x. Thanks!