Issue #1636992 by nod_, Wim Leers: Form.js' formUpdated event is unreliable/incomplete.

core/misc/form.js

-(function ($) {
+(function ($, Drupal, debounce) {
 
 "use strict";
 
@@ -116,6 +116,82 @@ Drupal.behaviors.formSingleSubmit = {
   }
 };
 
+
+/**
+ * Sends a 'formUpdated' event each time a form element is modified.
+ */
+function triggerFormUpdated (element) {
+ $(element).trigger('formUpdated');
+}
+
+/**
+ * Collects the IDs of all form fields in the given form.
+ *
+ * @param {HTMLFormElement} form
+ * @return {Array}
+ */
+function fieldsList (form) {
+  var $fieldList = $(form).find('[name]').map(function (index, element) {
+    // We use id to avoid name duplicates on radio fields and filter out
+    // elements with a name but no id.
+    return element.getAttribute('id');
+  });
+  // Return a true array.
+  return $.makeArray($fieldList);
+}
+
+/**
+ * Triggers the 'formUpdated' event on form elements when they are modified.
+ */
+Drupal.behaviors.formUpdated = {
+ attach: function (context) {
+   var $context = $(context);
+   var contextIsForm = $context.is('form');
+   var $forms = $context.find('form').once('form-updated');
+
+   if (contextIsForm) {
+     $forms = $context;
+   }
+
+   if ($forms.length) {
+     // Initialize form behaviors, use $.makeArray to be able to use native
+     // forEach array method and have the callback parameters in the right order.
+     $.makeArray($forms).forEach(function (form) {
+       var events = 'change.formUpdated keypress.formUpdated';
+       var eventHandler = debounce(function (event) { triggerFormUpdated(event.target); }, 300);
+       var formFields = fieldsList(form).join(',');
+
+       form.setAttribute('data-drupal-form-fields', formFields);
+       $(form).on(events, eventHandler);
+     });
+   }
+   // On ajax requests context is the form element.
+   if (contextIsForm) {
+    var formFields = fieldsList(context).join(',');
+    // @todo replace with form.getAttribute() when #1979468 is in.
+    var currentFields = $(context).attr('data-drupal-form-fields');
+    // if there has been a change in the fields or their order, trigger
+    // formUpdated.
+    if (formFields !== currentFields) {
+      triggerFormUpdated(context);
+    }
+  }
+
+ },
+ detach: function (context, settings, trigger) {
+   var $context = $(context);
+   if (trigger === 'unload') {
+     var $forms = $context.find('form').removeOnce('form-updated');
+     if ($forms.length) {
+       $.makeArray($forms).forEach(function (form) {
+         form.removeAttribute('data-drupal-form-fields');
+         $(form).off('.formUpdated');
+       });
+     }
+   }
+ }
+};
+
 /**
  * Prepopulate form fields with information from the visitor cookie.
  */
@@ -136,4 +212,4 @@ Drupal.behaviors.fillUserInfoFromCookie = {
   }
 };
 
-})(jQuery);
+})(jQuery, Drupal, Drupal.debounce);

core/modules/filter/filter.js

@@ -12,15 +12,22 @@
  */
 Drupal.behaviors.filterGuidelines = {
   attach: function (context) {
+
+    function updateFilterGuidelines (event) {
+      var $this = $(event.target);
+      var value = $this.val();
+      $this.closest('.filter-wrapper')
+        .find('.filter-guidelines-item').hide()
+        .filter('.filter-guidelines-' + value).show();
+    }
+
     $(context).find('.filter-guidelines').once('filter-guidelines')
       .find(':header').hide()
       .closest('.filter-wrapper').find('select.filter-list')
-      .on('change', function () {
-        $(this).closest('.filter-wrapper')
-          .find('.filter-guidelines-item').hide()
-          .filter('.filter-guidelines-' + this.value).show();
-      })
-      .trigger('change');
+      .on('change.filterGuidelines', updateFilterGuidelines)
+      // Need to trigger the namespaced event to avoid triggering formUpdated
+      // when initializing the select.
+      .trigger('change.filterGuidelines');
   }
 };
 

core/modules/system/system.module

@@ -959,6 +959,7 @@ function system_library_info() {
     'dependencies' => array(
       array('system', 'jquery'),
       array('system', 'drupal'),
+      array('system', 'drupal.debounce'),
       array('system', 'jquery.cookie'),
       array('system', 'jquery.once'),
     ),