Issue #2215857 followup by gaydamaka, timmillwood, alexpott, lauriii: Regression on Internet Explorer 11

(cherry picked from commit 266f3f9c1517e1b6b34891474a15f12dd3caa329)

Author: lauriii

misc/ajax.es6.js

@@ -774,7 +774,7 @@
     // when there is a form such that this.$form.ajaxSubmit() is used instead of
     // $.ajax(). When there is no form and $.ajax() is used, beforeSerialize()
     // isn't called, but don't rely on that: explicitly check this.$form.
-    if (this.$form && document.contains(this.$form.get(0))) {
+    if (this.$form && document.body.contains(this.$form.get(0))) {
       const settings = this.settings || drupalSettings;
       Drupal.detachBehaviors(this.$form.get(0), settings, 'serialize');
     }
@@ -1020,7 +1020,7 @@
     // attachBehaviors() called on the new content from processing the response
     // commands is not sufficient, because behaviors from the entire form need
     // to be reattached.
-    if (this.$form && document.contains(this.$form.get(0))) {
+    if (this.$form && document.body.contains(this.$form.get(0))) {
       const settings = this.settings || drupalSettings;
       Drupal.attachBehaviors(this.$form.get(0), settings);
     }
@@ -1090,7 +1090,7 @@
     $(this.element).prop('disabled', false);
     // Reattach behaviors, if they were detached in beforeSerialize(), and the
     // form is still part of the document.
-    if (this.$form && document.contains(this.$form.get(0))) {
+    if (this.$form && document.body.contains(this.$form.get(0))) {
       const settings = this.settings || drupalSettings;
       Drupal.attachBehaviors(this.$form.get(0), settings);
     }

misc/ajax.js

@@ -339,7 +339,7 @@ function _toConsumableArray(arr) { if (Array.isArray(arr)) { for (var i = 0, arr
   };
 
   Drupal.Ajax.prototype.beforeSerialize = function (element, options) {
-    if (this.$form && document.contains(this.$form.get(0))) {
+    if (this.$form && document.body.contains(this.$form.get(0))) {
       var settings = this.settings || drupalSettings;
       Drupal.detachBehaviors(this.$form.get(0), settings, 'serialize');
     }
@@ -451,7 +451,7 @@ function _toConsumableArray(arr) { if (Array.isArray(arr)) { for (var i = 0, arr
       }
     }
 
-    if (this.$form && document.contains(this.$form.get(0))) {
+    if (this.$form && document.body.contains(this.$form.get(0))) {
       var settings = this.settings || drupalSettings;
       Drupal.attachBehaviors(this.$form.get(0), settings);
     }
@@ -493,7 +493,7 @@ function _toConsumableArray(arr) { if (Array.isArray(arr)) { for (var i = 0, arr
 
     $(this.element).prop('disabled', false);
 
-    if (this.$form && document.contains(this.$form.get(0))) {
+    if (this.$form && document.body.contains(this.$form.get(0))) {
       var settings = this.settings || drupalSettings;
       Drupal.attachBehaviors(this.$form.get(0), settings);
     }