diff --git a/app/assets/javascripts/admin/addon/templates/badges-show.hbs b/app/assets/javascripts/admin/addon/templates/badges-show.hbs
index 1c88e9e4172..49741c8bc66 100644
--- a/app/assets/javascripts/admin/addon/templates/badges-show.hbs
+++ b/app/assets/javascripts/admin/addon/templates/badges-show.hbs
@@ -17,7 +17,7 @@
         options=(hash
           maximum=1
         )
-        onChange=(fn (mut buffered.icon))
+        onChange=(action (mut buffered.icon))
       }}
 
       <p class="help">{{i18n "admin.badges.icon_help"}}</p>
@@ -35,7 +35,7 @@
         name="badge_type_id"
         value=buffered.badge_type_id
         content=badgeTypes
-        onChange=(fn (mut buffered.badge_type_id))
+        onChange=(action (mut buffered.badge_type_id))
         isDisabled=readOnly
       }}
     </div>
@@ -50,7 +50,7 @@
           content=badgeGroupings
           class="badge-selector"
           nameProperty="name"
-          onChange=(fn (mut buffered.badge_grouping_id))
+          onChange=(action (mut buffered.badge_grouping_id))
         }}
         {{d-button
           class="btn-default"
@@ -112,7 +112,7 @@
             name="trigger"
             value=buffered.trigger
             content=badgeTriggers
-            onChange=(fn (mut buffered.trigger))
+            onChange=(action (mut buffered.trigger))
             disabled=readOnly
           }}
         </div>
diff --git a/app/assets/javascripts/admin/addon/templates/components/admin-user-field-item.hbs b/app/assets/javascripts/admin/addon/templates/components/admin-user-field-item.hbs
index 7414446097b..211cc00b516 100644
--- a/app/assets/javascripts/admin/addon/templates/components/admin-user-field-item.hbs
+++ b/app/assets/javascripts/admin/addon/templates/components/admin-user-field-item.hbs
@@ -3,7 +3,7 @@
     {{combo-box
       content=fieldTypes
       value=buffered.field_type
-      onChange=(fn (mut buffered.field_type))
+      onChange=(action (mut buffered.field_type))
     }}
   {{/admin-form-row}}
 
diff --git a/app/assets/javascripts/admin/addon/templates/components/embeddable-host.hbs b/app/assets/javascripts/admin/addon/templates/components/embeddable-host.hbs
index 1ed3212d6ff..7d73d93a2b3 100644
--- a/app/assets/javascripts/admin/addon/templates/components/embeddable-host.hbs
+++ b/app/assets/javascripts/admin/addon/templates/components/embeddable-host.hbs
@@ -16,7 +16,7 @@
     {{category-chooser
       value=categoryId
       class="small"
-      onChange=(mut categoryId)
+      onChange=(action (mut categoryId))
     }}
   </td>
   <td class="editing-controls">
diff --git a/app/assets/javascripts/admin/addon/templates/components/permalink-form.hbs b/app/assets/javascripts/admin/addon/templates/components/permalink-form.hbs
index f8ec83bfd2a..8792d78734c 100644
--- a/app/assets/javascripts/admin/addon/templates/components/permalink-form.hbs
+++ b/app/assets/javascripts/admin/addon/templates/components/permalink-form.hbs
@@ -11,7 +11,7 @@
 {{combo-box
   content=permalinkTypes
   value=permalinkType
-  onChange=(mut permalinkType)
+  onChange=(action (mut permalinkType))
   class="permalink-type"
 }}
 
diff --git a/app/assets/javascripts/admin/addon/templates/components/screened-ip-address-form.hbs b/app/assets/javascripts/admin/addon/templates/components/screened-ip-address-form.hbs
index aa9da28f0c1..488c14fb5ff 100644
--- a/app/assets/javascripts/admin/addon/templates/components/screened-ip-address-form.hbs
+++ b/app/assets/javascripts/admin/addon/templates/components/screened-ip-address-form.hbs
@@ -4,7 +4,7 @@
 {{combo-box
   content=actionNames
   value=actionName
-  onChange=(mut actionName)
+  onChange=(action (mut actionName))
 }}
 
 {{d-button class="btn-default" action=(action "submit") disabled=formSubmitted label="admin.logs.screened_ips.form.add"}}
diff --git a/app/assets/javascripts/admin/addon/templates/components/site-settings/category.hbs b/app/assets/javascripts/admin/addon/templates/components/site-settings/category.hbs
index 089e590256d..80a793834ea 100644
--- a/app/assets/javascripts/admin/addon/templates/components/site-settings/category.hbs
+++ b/app/assets/javascripts/admin/addon/templates/components/site-settings/category.hbs
@@ -1,7 +1,7 @@
 {{category-chooser
   value=value
   allowUncategorized=true
-  onChange=(mut value)
+  onChange=(action (mut value))
 }}
 {{setting-validation-message message=validationMessage}}
 <div class="desc">{{html-safe setting.description}}</div>
diff --git a/app/assets/javascripts/admin/addon/templates/components/site-settings/enum.hbs b/app/assets/javascripts/admin/addon/templates/components/site-settings/enum.hbs
index be5f5cc7464..265301db6a4 100644
--- a/app/assets/javascripts/admin/addon/templates/components/site-settings/enum.hbs
+++ b/app/assets/javascripts/admin/addon/templates/components/site-settings/enum.hbs
@@ -1,7 +1,7 @@
 {{combo-box
   content=setting.validValues
   value=value
-  onChange=(mut value)
+  onChange=(action (mut value))
   valueProperty=setting.computedValueProperty
   nameProperty=setting.computedNameProperty
   options=(hash
diff --git a/app/assets/javascripts/admin/addon/templates/modal/admin-color-scheme-select-base.hbs b/app/assets/javascripts/admin/addon/templates/modal/admin-color-scheme-select-base.hbs
index 0d18c2656e4..15a39314cd3 100644
--- a/app/assets/javascripts/admin/addon/templates/modal/admin-color-scheme-select-base.hbs
+++ b/app/assets/javascripts/admin/addon/templates/modal/admin-color-scheme-select-base.hbs
@@ -4,7 +4,7 @@
     {{combo-box
       content=model
       value=selectedBaseThemeId
-      onChange=(mut selectedBaseThemeId)
+      onChange=(action (mut selectedBaseThemeId))
       valueProperty="base_scheme_id"
     }}
   {{/d-modal-body}}
diff --git a/app/assets/javascripts/admin/addon/templates/modal/admin-install-theme.hbs b/app/assets/javascripts/admin/addon/templates/modal/admin-install-theme.hbs
index d0c607b7f5c..053ce042a8c 100644
--- a/app/assets/javascripts/admin/addon/templates/modal/admin-install-theme.hbs
+++ b/app/assets/javascripts/admin/addon/templates/modal/admin-install-theme.hbs
@@ -93,7 +93,7 @@
           valueProperty="value"
           content=createTypes
           value=selectedType
-          onChange=(mut selectedType)
+          onChange=(action (mut selectedType))
         }}
       </div>
     {{/if}}
diff --git a/app/assets/javascripts/admin/addon/templates/search-logs-index.hbs b/app/assets/javascripts/admin/addon/templates/search-logs-index.hbs
index aafdf2aab9b..baf516489d8 100644
--- a/app/assets/javascripts/admin/addon/templates/search-logs-index.hbs
+++ b/app/assets/javascripts/admin/addon/templates/search-logs-index.hbs
@@ -1,10 +1,10 @@
 <div class="admin-title">
-  {{period-chooser period=period onChange=(mut period)}}
+  {{period-chooser period=period onChange=(action (mut period))}}
   {{combo-box
     content=searchTypeOptions
     value=searchType
     class="search-logs-filter"
-    onChange=(mut searchType)
+    onChange=(action (mut searchType))
   }}
 </div>
 
diff --git a/app/assets/javascripts/admin/addon/templates/search-logs-term.hbs b/app/assets/javascripts/admin/addon/templates/search-logs-term.hbs
index 43753b1e39a..b4b0c8aed3e 100644
--- a/app/assets/javascripts/admin/addon/templates/search-logs-term.hbs
+++ b/app/assets/javascripts/admin/addon/templates/search-logs-term.hbs
@@ -1,10 +1,10 @@
 <div class="admin-title">
-  {{period-chooser period=period onChange=(mut period)}}
+  {{period-chooser period=period onChange=(action (mut period))}}
   {{combo-box
     content=searchTypeOptions
     value=searchType
     class="search-logs-filter"
-    onChange=(mut searchType)
+    onChange=(action (mut searchType))
   }}
 </div>
 
diff --git a/app/assets/javascripts/admin/addon/templates/user-badges.hbs b/app/assets/javascripts/admin/addon/templates/user-badges.hbs
index ecf30a1b867..a5e66640d3c 100644
--- a/app/assets/javascripts/admin/addon/templates/user-badges.hbs
+++ b/app/assets/javascripts/admin/addon/templates/user-badges.hbs
@@ -20,7 +20,7 @@
             filterable=true
             value=selectedBadgeId
             content=grantableBadges
-            onChange=(mut selectedBadgeId)
+            onChange=(action (mut selectedBadgeId))
           }}
         </div>
         <div>
diff --git a/app/assets/javascripts/admin/addon/templates/user-index.hbs b/app/assets/javascripts/admin/addon/templates/user-index.hbs
index 31f979a753f..c043ce529f1 100644
--- a/app/assets/javascripts/admin/addon/templates/user-index.hbs
+++ b/app/assets/javascripts/admin/addon/templates/user-index.hbs
@@ -371,7 +371,7 @@
         content=site.trustLevels
         nameProperty="detailedName"
         value=model.trustLevel.id
-        onChange=(mut model.trust_level)
+        onChange=(action (mut model.trust_level))
       }}
 
       {{#if model.dirty}}
@@ -537,7 +537,7 @@
           content=availableGroups
           value=customGroupIdsBuffer
           labelProperty="name"
-          onChange=(fn (mut customGroupIdsBuffer))
+          onChange=(action (mut customGroupIdsBuffer))
         }}
       </div>
       {{#if customGroupsDirty}}
@@ -555,7 +555,7 @@
             content=model.customGroups
             value=model.primary_group_id
             none="admin.groups.no_primary"
-            onChange=(mut model.primary_group_id)
+            onChange=(action (mut model.primary_group_id))
           }}
         </div>
         {{#if primaryGroupDirty}}
diff --git a/app/assets/javascripts/admin/addon/templates/web-hooks-show.hbs b/app/assets/javascripts/admin/addon/templates/web-hooks-show.hbs
index 1c7e97beb37..83540a03da4 100644
--- a/app/assets/javascripts/admin/addon/templates/web-hooks-show.hbs
+++ b/app/assets/javascripts/admin/addon/templates/web-hooks-show.hbs
@@ -18,7 +18,7 @@
         content=contentTypes
         name="content-type"
         value=model.content_type
-        onChange=(mut model.content_type)
+        onChange=(action (mut model.content_type))
       }}
     </div>
 
@@ -53,7 +53,7 @@
         <label>{{d-icon "circle" class="tracking"}}{{i18n "admin.web_hooks.categories_filter"}}</label>
         {{category-selector
           categories=model.categories
-          onChange=(mut model.categories)
+          onChange=(action (mut model.categories))
         }}
         <div class="instructions">{{i18n "admin.web_hooks.categories_filter_instructions"}}</div>
       </div>
diff --git a/app/assets/javascripts/discourse/app/templates/components/badge-title.hbs b/app/assets/javascripts/discourse/app/templates/components/badge-title.hbs
index 81b1dc7a8e7..de1e7fbafac 100644
--- a/app/assets/javascripts/discourse/app/templates/components/badge-title.hbs
+++ b/app/assets/javascripts/discourse/app/templates/components/badge-title.hbs
@@ -13,7 +13,7 @@
           value=selectedUserBadgeId
           nameProperty="badge.name"
           content=selectableUserBadges
-          onChange=(fn (mut selectedUserBadgeId))
+          onChange=(action (mut selectedUserBadgeId))
         }}
       </div>
     </div>
diff --git a/app/assets/javascripts/discourse/app/templates/components/edit-category-general.hbs b/app/assets/javascripts/discourse/app/templates/components/edit-category-general.hbs
index 05ff39de9fe..23e2981f000 100644
--- a/app/assets/javascripts/discourse/app/templates/components/edit-category-general.hbs
+++ b/app/assets/javascripts/discourse/app/templates/components/edit-category-general.hbs
@@ -19,7 +19,7 @@
         allowSubCategories=true
         allowUncategorized=false
         allowRestrictedCategories=true
-        onChange=(fn (mut category.parent_category_id))
+        onChange=(action (mut category.parent_category_id))
       }}
     </section>
   {{/if}}
diff --git a/app/assets/javascripts/discourse/app/templates/components/edit-category-settings.hbs b/app/assets/javascripts/discourse/app/templates/components/edit-category-settings.hbs
index c8cda21a940..f847963bfcf 100644
--- a/app/assets/javascripts/discourse/app/templates/components/edit-category-settings.hbs
+++ b/app/assets/javascripts/discourse/app/templates/components/edit-category-settings.hbs
@@ -38,7 +38,7 @@
         id="category-search-priority"
         content=searchPrioritiesOptions
         value=category.search_priority
-        onChange=(mut category.search_priority)
+        onChange=(action (mut category.search_priority))
         options=(hash
           placementStrategy="absolute"
         )
@@ -190,7 +190,7 @@
         options=(hash
           none="category.sort_options.default"
         )
-        onChange=(mut category.sort_order)
+        onChange=(action (mut category.sort_order))
       }}
       {{#unless isDefaultSortOrder}}
         {{combo-box
@@ -201,7 +201,7 @@
             none="category.sort_options.default"
             placementStrategy="absolute"
           )
-          onChange=(mut category.sort_ascending)
+          onChange=(action (mut category.sort_ascending))
         }}
       {{/unless}}
     </div>
diff --git a/app/assets/javascripts/discourse/app/templates/components/edit-category-tags.hbs b/app/assets/javascripts/discourse/app/templates/components/edit-category-tags.hbs
index 405b1448512..6fcb4bded0b 100644
--- a/app/assets/javascripts/discourse/app/templates/components/edit-category-tags.hbs
+++ b/app/assets/javascripts/discourse/app/templates/components/edit-category-tags.hbs
@@ -6,7 +6,7 @@
     everyTag=true
     excludeSynonyms=true
     unlimitedTagCount=true
-    onChange=(mut category.allowed_tags)
+    onChange=(action (mut category.allowed_tags))
     options=(hash
       filterPlaceholder="category.tags_placeholder"
     )
diff --git a/app/assets/javascripts/discourse/app/templates/components/edit-topic-timer-form.hbs b/app/assets/javascripts/discourse/app/templates/components/edit-topic-timer-form.hbs
index a5a50503cd6..0303a494a62 100644
--- a/app/assets/javascripts/discourse/app/templates/components/edit-topic-timer-form.hbs
+++ b/app/assets/javascripts/discourse/app/templates/components/edit-topic-timer-form.hbs
@@ -13,7 +13,7 @@
       {{category-chooser
         value=topicTimer.category_id
         excludeCategoryId=excludeCategoryId
-        onChange=(fn (mut topicTimer.category_id))
+        onChange=(action (mut topicTimer.category_id))
       }}
     </div>
   {{/if}}
diff --git a/app/assets/javascripts/discourse/app/templates/components/group-flair-inputs.hbs b/app/assets/javascripts/discourse/app/templates/components/group-flair-inputs.hbs
index 6203f330086..f198b7bb636 100644
--- a/app/assets/javascripts/discourse/app/templates/components/group-flair-inputs.hbs
+++ b/app/assets/javascripts/discourse/app/templates/components/group-flair-inputs.hbs
@@ -18,7 +18,7 @@
       name="icon"
       value=model.flair_icon
       options=(hash maximum=1)
-      onChange=(mut model.flair_icon)
+      onChange=(action (mut model.flair_icon))
     }}
   {{else if flairPreviewImage}}
     {{image-uploader
diff --git a/app/assets/javascripts/discourse/app/templates/components/groups-form-email-fields.hbs b/app/assets/javascripts/discourse/app/templates/components/groups-form-email-fields.hbs
index 6a4a49b905d..555282097f0 100644
--- a/app/assets/javascripts/discourse/app/templates/components/groups-form-email-fields.hbs
+++ b/app/assets/javascripts/discourse/app/templates/components/groups-form-email-fields.hbs
@@ -63,7 +63,7 @@
                   valueProperty="value"
                   content=mailboxes
                   none="groups.manage.email.mailboxes.disabled"
-                  onChange=(mut model.imap_mailbox_name)}}
+                  onChange=(action (mut model.imap_mailbox_name))}}
     {{else}}
       {{i18n "groups.manage.email.mailboxes.none_found"}}
     {{/if}}
diff --git a/app/assets/javascripts/discourse/app/templates/components/groups-form-interaction-fields.hbs b/app/assets/javascripts/discourse/app/templates/components/groups-form-interaction-fields.hbs
index 0ba572897a7..80d0b147547 100644
--- a/app/assets/javascripts/discourse/app/templates/components/groups-form-interaction-fields.hbs
+++ b/app/assets/javascripts/discourse/app/templates/components/groups-form-interaction-fields.hbs
@@ -10,7 +10,7 @@
       content=visibilityLevelOptions
       castInteger=true
       class="groups-form-visibility-level"
-      onChange=(mut model.visibility_level)
+      onChange=(action (mut model.visibility_level))
     }}
 
     <div class="control-instructions">
@@ -26,7 +26,7 @@
       value=membersVisibilityLevel
       content=visibilityLevelOptions
       class="groups-form-members-visibility-level"
-      onChange=(mut model.members_visibility_level)
+      onChange=(action (mut model.members_visibility_level))
     }}
 
     <div class="control-instructions">
@@ -45,7 +45,7 @@
     value=mentionableLevel
     content=aliasLevelOptions
     class="groups-form-mentionable-level"
-    onChange=(mut model.mentionable_level)
+    onChange=(action (mut model.mentionable_level))
   }}
 </div>
 
@@ -58,7 +58,7 @@
     value=messageableLevel
     content=aliasLevelOptions
     class="groups-form-messageable-level"
-    onChange=(mut model.messageable_level)
+    onChange=(action (mut model.messageable_level))
   }}
 </div>
 
diff --git a/app/assets/javascripts/discourse/app/templates/components/groups-form-membership-fields.hbs b/app/assets/javascripts/discourse/app/templates/components/groups-form-membership-fields.hbs
index 09a5180845b..03a6813bf2c 100644
--- a/app/assets/javascripts/discourse/app/templates/components/groups-form-membership-fields.hbs
+++ b/app/assets/javascripts/discourse/app/templates/components/groups-form-membership-fields.hbs
@@ -32,7 +32,7 @@
       value=groupTrustLevel
       content=trustLevelOptions
       class="groups-form-grant-trust-level"
-      onChange=(mut model.grant_trust_level)
+      onChange=(action (mut model.grant_trust_level))
     }}
     <label>
       {{input type="checkbox"
diff --git a/app/assets/javascripts/discourse/app/templates/components/invite-link-panel.hbs b/app/assets/javascripts/discourse/app/templates/components/invite-link-panel.hbs
index 5e5230a5793..270df195b76 100644
--- a/app/assets/javascripts/discourse/app/templates/components/invite-link-panel.hbs
+++ b/app/assets/javascripts/discourse/app/templates/components/invite-link-panel.hbs
@@ -18,7 +18,7 @@
           content=allGroups
           value=groupIds
           labelProperty="name"
-          onChange=(mut groupIds)}}
+          onChange=(action (mut groupIds))}}
       </div>
     {{/if}}
 
diff --git a/app/assets/javascripts/discourse/app/templates/components/invite-panel.hbs b/app/assets/javascripts/discourse/app/templates/components/invite-panel.hbs
index 4b8c9afa779..ea571e60927 100644
--- a/app/assets/javascripts/discourse/app/templates/components/invite-panel.hbs
+++ b/app/assets/javascripts/discourse/app/templates/components/invite-panel.hbs
@@ -57,7 +57,7 @@
           content=allGroups
           value=groupIds
           labelProperty="name"
-          onChange=(mut groupIds)
+          onChange=(action (mut groupIds))
         }}
       </div>
     {{/if}}
diff --git a/app/assets/javascripts/discourse/app/templates/components/user-fields/dropdown.hbs b/app/assets/javascripts/discourse/app/templates/components/user-fields/dropdown.hbs
index 070f7de3a95..f34fe5267b7 100644
--- a/app/assets/javascripts/discourse/app/templates/components/user-fields/dropdown.hbs
+++ b/app/assets/javascripts/discourse/app/templates/components/user-fields/dropdown.hbs
@@ -13,7 +13,7 @@
     nameProperty=null
     value=this.value
     none=this.noneLabel
-    onChange=(fn (mut this.value))
+    onChange=(action (mut this.value))
   }}
   <div class="instructions">{{html-safe this.field.description}}</div>
 </div>
diff --git a/app/assets/javascripts/discourse/app/templates/composer.hbs b/app/assets/javascripts/discourse/app/templates/composer.hbs
index 313d686f093..ded30ce02a8 100644
--- a/app/assets/javascripts/discourse/app/templates/composer.hbs
+++ b/app/assets/javascripts/discourse/app/templates/composer.hbs
@@ -75,7 +75,7 @@
                     {{category-chooser
                       value=model.categoryId
                       tabindex="3"
-                      onChange=(fn (mut model.categoryId))
+                      onChange=(action (mut model.categoryId))
                       isDisabled=disableCategoryChooser
                       options=(hash
                         scopedCategoryId=scopedCategoryId
@@ -89,7 +89,7 @@
                     value=model.tags
                     tabindex=4
                     isDisabled=disableTagsChooser
-                    onChange=(fn (mut model.tags))
+                    onChange=(action (mut model.tags))
                     options=(hash
                       categoryId=model.categoryId
                       minimum=model.minimumRequiredTags
diff --git a/app/assets/javascripts/discourse/app/templates/full-page-search.hbs b/app/assets/javascripts/discourse/app/templates/full-page-search.hbs
index 7a85aa6d90b..f95bc36dc71 100644
--- a/app/assets/javascripts/discourse/app/templates/full-page-search.hbs
+++ b/app/assets/javascripts/discourse/app/templates/full-page-search.hbs
@@ -59,7 +59,7 @@
             value=sortOrder
             content=sortOrders
             castInteger=true
-            onChange=(mut sortOrder)
+            onChange=(action (mut sortOrder))
           }}
         </div>
       </div>
@@ -213,7 +213,7 @@
         <div class="search-advanced-filters">
           {{search-advanced-options
             searchTerm=(readonly searchTerm)
-            onChangeSearchTerm=(fn (mut searchTerm))
+            onChangeSearchTerm=(action (mut searchTerm))
           }}
         </div>
       {{/if}}
@@ -221,8 +221,8 @@
       <div class="search-advanced-filters">
         {{search-advanced-options
           searchTerm=(readonly searchTerm)
-          onChangeSearchTerm=(fn (mut searchTerm))
-          onChangeCategory=(fn (mut category))
+          onChangeSearchTerm=(action (mut searchTerm))
+          onChangeCategory=(action (mut category))
         }}
 
         {{d-button
diff --git a/app/assets/javascripts/discourse/app/templates/group/manage/categories.hbs b/app/assets/javascripts/discourse/app/templates/group/manage/categories.hbs
index 197c77108cf..23de93eb10c 100644
--- a/app/assets/javascripts/discourse/app/templates/group/manage/categories.hbs
+++ b/app/assets/javascripts/discourse/app/templates/group/manage/categories.hbs
@@ -10,7 +10,7 @@
     {{category-selector
       categories=model.watchingCategories
       blockedCategories=selectedCategories
-      onChange=(mut model.watchingCategories)
+      onChange=(action (mut model.watchingCategories))
     }}
 
     <div class="control-instructions">
@@ -24,7 +24,7 @@
     {{category-selector
       categories=model.trackingCategories
       blockedCategories=selectedCategories
-      onChange=(mut model.trackingCategories)
+      onChange=(action (mut model.trackingCategories))
     }}
 
     <div class="control-instructions">
@@ -38,7 +38,7 @@
     {{category-selector
       categories=model.watchingFirstPostCategories
       blockedCategories=selectedCategories
-      onChange=(mut model.watchingFirstPostCategories)
+      onChange=(action (mut model.watchingFirstPostCategories))
     }}
 
     <div class="control-instructions">
@@ -52,7 +52,7 @@
     {{category-selector
       categories=model.regularCategories
       blockedCategories=selectedCategories
-      onChange=(mut model.regularCategories)
+      onChange=(action (mut model.regularCategories))
     }}
 
     <div class="control-instructions">
@@ -66,7 +66,7 @@
     {{category-selector
       categories=model.mutedCategories
       blockedCategories=selectedCategories
-      onChange=(mut model.mutedCategories)
+      onChange=(action (mut model.mutedCategories))
     }}
 
     <div class="control-instructions">
diff --git a/app/assets/javascripts/discourse/app/templates/groups/index.hbs b/app/assets/javascripts/discourse/app/templates/groups/index.hbs
index ded481bf8bb..5abcf07eeb9 100644
--- a/app/assets/javascripts/discourse/app/templates/groups/index.hbs
+++ b/app/assets/javascripts/discourse/app/templates/groups/index.hbs
@@ -21,7 +21,7 @@
         value=type
         content=types
         class="groups-header-filters-type"
-        onChange=(mut type)
+        onChange=(action (mut type))
         options=(hash
           clearable=true
           none="groups.index.filter"
diff --git a/app/assets/javascripts/discourse/app/templates/mobile/users.hbs b/app/assets/javascripts/discourse/app/templates/mobile/users.hbs
index 1fa9ae7d81e..e7f3884e520 100644
--- a/app/assets/javascripts/discourse/app/templates/mobile/users.hbs
+++ b/app/assets/javascripts/discourse/app/templates/mobile/users.hbs
@@ -4,7 +4,7 @@
       {{plugin-outlet name="users-top" connectorTagName="div" args=(hash model=model)}}
 
       <div class="directory-controls">
-        {{period-chooser period=period onChange=(mut period) fullDay=false}}
+        {{period-chooser period=period onChange=(action (mut period)) fullDay=false}}
         {{#if lastUpdatedAt}}
           <div class="directory-last-updated">
             {{i18n "directory.last_updated"}}
diff --git a/app/assets/javascripts/discourse/app/templates/modal/bookmark.hbs b/app/assets/javascripts/discourse/app/templates/modal/bookmark.hbs
index 945ace3faa4..59bd6ebb69c 100644
--- a/app/assets/javascripts/discourse/app/templates/modal/bookmark.hbs
+++ b/app/assets/javascripts/discourse/app/templates/modal/bookmark.hbs
@@ -19,7 +19,7 @@
         content=autoDeletePreferences
         value=autoDeletePreference
         class="bookmark-option-selector"
-        onChange=(fn (mut autoDeletePreference))
+        onChange=(action (mut autoDeletePreference))
       }}
     </div>
 
diff --git a/app/assets/javascripts/discourse/app/templates/modal/bulk-change-category.hbs b/app/assets/javascripts/discourse/app/templates/modal/bulk-change-category.hbs
index a9f83e5864a..005b266389a 100644
--- a/app/assets/javascripts/discourse/app/templates/modal/bulk-change-category.hbs
+++ b/app/assets/javascripts/discourse/app/templates/modal/bulk-change-category.hbs
@@ -3,7 +3,7 @@
 <p>
   {{category-chooser
     value=newCategoryId
-    onChange=(mut newCategoryId)
+    onChange=(action (mut newCategoryId))
   }}
 </p>
 
diff --git a/app/assets/javascripts/discourse/app/templates/modal/convert-to-public-topic.hbs b/app/assets/javascripts/discourse/app/templates/modal/convert-to-public-topic.hbs
index 90586aa58e2..314a5478f52 100644
--- a/app/assets/javascripts/discourse/app/templates/modal/convert-to-public-topic.hbs
+++ b/app/assets/javascripts/discourse/app/templates/modal/convert-to-public-topic.hbs
@@ -5,7 +5,7 @@
   </div>
   {{category-chooser
     value=publicCategoryId
-    onChange=(mut publicCategoryId)
+    onChange=(action (mut publicCategoryId))
   }}
 
 {{/d-modal-body}}
diff --git a/app/assets/javascripts/discourse/app/templates/modal/grant-badge.hbs b/app/assets/javascripts/discourse/app/templates/modal/grant-badge.hbs
index 2eccc044a01..4a4d4646901 100644
--- a/app/assets/javascripts/discourse/app/templates/modal/grant-badge.hbs
+++ b/app/assets/javascripts/discourse/app/templates/modal/grant-badge.hbs
@@ -9,7 +9,7 @@
           value=selectedBadgeId
           content=grantableBadges
           none="badges.none"
-          onChange=(mut selectedBadgeId)
+          onChange=(action (mut selectedBadgeId))
         }}
       </p>
     {{/if}}
diff --git a/app/assets/javascripts/discourse/app/templates/modal/move-to-topic.hbs b/app/assets/javascripts/discourse/app/templates/modal/move-to-topic.hbs
index f3bff90ff06..6386cecd2a6 100644
--- a/app/assets/javascripts/discourse/app/templates/modal/move-to-topic.hbs
+++ b/app/assets/javascripts/discourse/app/templates/modal/move-to-topic.hbs
@@ -81,7 +81,7 @@
           {{category-chooser
             value=categoryId
             class="small"
-            onChange=(mut categoryId)
+            onChange=(action (mut categoryId))
           }}
           {{#if canAddTags}}
             <label>{{i18n "tagging.tags"}}</label>
diff --git a/app/assets/javascripts/discourse/app/templates/preferences/account.hbs b/app/assets/javascripts/discourse/app/templates/preferences/account.hbs
index 306fb02dd59..ed380319ff6 100644
--- a/app/assets/javascripts/discourse/app/templates/preferences/account.hbs
+++ b/app/assets/javascripts/discourse/app/templates/preferences/account.hbs
@@ -189,7 +189,7 @@
         value=newTitleInput
         content=model.availableTitles
         none="user.title.none"
-        onChange=(mut newTitleInput)
+        onChange=(action (mut newTitleInput))
       }}
     </div>
   </div>
diff --git a/app/assets/javascripts/discourse/app/templates/preferences/categories.hbs b/app/assets/javascripts/discourse/app/templates/preferences/categories.hbs
index 40cb2c34094..41347d2caec 100644
--- a/app/assets/javascripts/discourse/app/templates/preferences/categories.hbs
+++ b/app/assets/javascripts/discourse/app/templates/preferences/categories.hbs
@@ -9,7 +9,7 @@
     {{category-selector
       categories=model.watchedCategories
       blockedCategories=selectedCategories
-      onChange=(mut model.watchedCategories)
+      onChange=(action (mut model.watchedCategories))
     }}
   </div>
   <div class="instructions">{{i18n "user.watched_categories_instructions"}}</div>
@@ -22,7 +22,7 @@
     {{category-selector
       categories=model.trackedCategories
       blockedCategories=selectedCategories
-      onChange=(mut model.trackedCategories)
+      onChange=(action (mut model.trackedCategories))
     }}
   </div>
   <div class="instructions">{{i18n "user.tracked_categories_instructions"}}</div>
@@ -32,7 +32,7 @@
     {{category-selector
       categories=model.watchedFirstPostCategories
       blockedCategories=selectedCategories
-      onChange=(mut model.watchedFirstPostCategories)
+      onChange=(action (mut model.watchedFirstPostCategories))
     }}
   </div>
   <div class="instructions">{{i18n "user.watched_first_post_categories_instructions"}}</div>
@@ -43,7 +43,7 @@
       {{category-selector
         categories=model.regularCategories
         blockedCategories=selectedCategories
-        onChange=(mut model.regularCategories)
+        onChange=(action (mut model.regularCategories))
       }}
     </div>
     <div class="instructions">{{i18n "user.regular_categories_instructions"}}</div>
@@ -56,7 +56,7 @@
       {{category-selector
         categories=model.mutedCategories
         blockedCategories=selectedCategories
-        onChange=(mut model.mutedCategories)
+        onChange=(action (mut model.mutedCategories))
       }}
     </div>
     <div class="instructions">{{i18n (if hideMutedTags "user.muted_categories_instructions" "user.muted_categories_instructions_dont_hide")}}</div>
diff --git a/app/assets/javascripts/discourse/app/templates/preferences/emails.hbs b/app/assets/javascripts/discourse/app/templates/preferences/emails.hbs
index 5cd3f2e73e5..d5850f3ad14 100644
--- a/app/assets/javascripts/discourse/app/templates/preferences/emails.hbs
+++ b/app/assets/javascripts/discourse/app/templates/preferences/emails.hbs
@@ -15,7 +15,7 @@
       content=emailLevelOptions
       value=model.user_option.email_messages_level
       id="user-email-messages-level"
-      onChange=(mut model.user_option.email_messages_level)
+      onChange=(action (mut model.user_option.email_messages_level))
     }}
     {{#if emailMessagesLevelAway}}
       <div class="instructions">{{emailFrequencyInstructions}}</div>
@@ -29,7 +29,7 @@
       content=emailLevelOptions
       value=model.user_option.email_level
       id="user-email-level"
-      onChange=(mut model.user_option.email_level)
+      onChange=(action (mut model.user_option.email_level))
     }}
     {{#if emailLevelAway}}
       <div class="instructions">{{emailFrequencyInstructions}}</div>
@@ -42,7 +42,7 @@
       valueProperty="value"
       content=previousRepliesOptions
       value=model.user_option.email_previous_replies
-      onChange=(mut model.user_option.email_previous_replies)
+      onChange=(action (mut model.user_option.email_previous_replies))
     }}
   </div>
   {{preference-checkbox labelKey="user.email_in_reply_to" checked=model.user_option.email_in_reply_to}}
@@ -61,7 +61,7 @@
           filterable=true
           content=digestFrequencies
           value=model.user_option.digest_after_minutes
-          onChange=(mut model.user_option.digest_after_minutes)
+          onChange=(action (mut model.user_option.digest_after_minutes))
         }}
       </div>
       {{preference-checkbox labelKey="user.include_tl0_in_digests" disabled=model.user_option.mailing_list_mode checked=model.user_option.include_tl0_in_digests}}
@@ -80,7 +80,7 @@
           valueProperty="value"
           content=mailingListModeOptions
           value=model.user_option.mailing_list_mode_frequency
-          onChange=(mut model.user_option.mailing_list_mode_frequency)
+          onChange=(action (mut model.user_option.mailing_list_mode_frequency))
         }}
       </div>
     {{/if}}
diff --git a/app/assets/javascripts/discourse/app/templates/preferences/interface.hbs b/app/assets/javascripts/discourse/app/templates/preferences/interface.hbs
index d5bcdd9cfc2..e53cd172c2c 100644
--- a/app/assets/javascripts/discourse/app/templates/preferences/interface.hbs
+++ b/app/assets/javascripts/discourse/app/templates/preferences/interface.hbs
@@ -101,7 +101,7 @@
         valueProperty="value"
         content=availableLocales
         value=model.locale
-        onChange=(fn (mut model.locale))
+        onChange=(action (mut model.locale))
         options=(hash
           filterable=true
           none="user.locale.default"
@@ -121,7 +121,7 @@
       content=userSelectableHome
       valueProperty="value"
       value=homepageId
-      onChange=(fn (mut model.user_option.homepage_id))
+      onChange=(action (mut model.user_option.homepage_id))
     }}
   </div>
 </div>
@@ -147,7 +147,7 @@
       content=titleCountModes
       value=model.user_option.title_count_mode
       id="user-title-count-mode"
-      onChange=(fn (mut model.user_option.title_count_mode))
+      onChange=(action (mut model.user_option.title_count_mode))
     }}
   </div>
   {{preference-checkbox labelKey="user.skip_new_user_tips.description" checked=model.user_option.skip_new_user_tips  class="pref-new-user-tips"}}
diff --git a/app/assets/javascripts/discourse/app/templates/preferences/notifications.hbs b/app/assets/javascripts/discourse/app/templates/preferences/notifications.hbs
index e681dbd5941..ad3b52e8a33 100644
--- a/app/assets/javascripts/discourse/app/templates/preferences/notifications.hbs
+++ b/app/assets/javascripts/discourse/app/templates/preferences/notifications.hbs
@@ -8,7 +8,7 @@
       valueProperty="value"
       content=considerNewTopicOptions
       value=model.user_option.new_topic_duration_minutes
-      onChange=(mut model.user_option.new_topic_duration_minutes)
+      onChange=(action (mut model.user_option.new_topic_duration_minutes))
     }}
   </div>
 
@@ -18,7 +18,7 @@
       valueProperty="value"
       content=autoTrackDurations
       value=model.user_option.auto_track_topics_after_msecs
-      onChange=(mut model.user_option.auto_track_topics_after_msecs)
+      onChange=(action (mut model.user_option.auto_track_topics_after_msecs))
     }}
   </div>
 
@@ -28,7 +28,7 @@
       valueProperty="value"
       content=notificationLevelsForReplying
       value=model.user_option.notification_level_when_replying
-      onChange=(mut model.user_option.notification_level_when_replying)
+      onChange=(action (mut model.user_option.notification_level_when_replying))
     }}
   </div>
 
@@ -38,7 +38,7 @@
       valueProperty="value"
       content=likeNotificationFrequencies
       value=model.user_option.like_notification_frequency
-      onChange=(mut model.user_option.like_notification_frequency)
+      onChange=(action (mut model.user_option.like_notification_frequency))
     }}
   </div>
 </div>
diff --git a/app/assets/javascripts/discourse/app/templates/preferences/profile.hbs b/app/assets/javascripts/discourse/app/templates/preferences/profile.hbs
index 771ad7a8674..66e2a81afe8 100644
--- a/app/assets/javascripts/discourse/app/templates/preferences/profile.hbs
+++ b/app/assets/javascripts/discourse/app/templates/preferences/profile.hbs
@@ -11,7 +11,7 @@
   <label class="control-label">{{i18n "user.timezone"}}</label>
   {{timezone-input
     value=model.user_option.timezone
-    onChange=(mut model.user_option.timezone)
+    onChange=(action (mut model.user_option.timezone))
     class="input-xxlarge"
   }}
   {{d-button icon="globe" label="user.use_current_timezone" action=(action "useCurrentTimezone") }}
diff --git a/app/assets/javascripts/discourse/app/templates/review-index.hbs b/app/assets/javascripts/discourse/app/templates/review-index.hbs
index ffa6b29acd9..c5a0fad8891 100644
--- a/app/assets/javascripts/discourse/app/templates/review-index.hbs
+++ b/app/assets/javascripts/discourse/app/templates/review-index.hbs
@@ -22,7 +22,7 @@
       {{combo-box
         value=filterStatus
         content=statuses
-        onChange=(mut filterStatus)
+        onChange=(action (mut filterStatus))
       }}
     </div>
 
@@ -36,7 +36,7 @@
           value=filterType
           content=allTypes
           none="review.filters.type.all"
-          onChange=(mut filterType)
+          onChange=(action (mut filterType))
         }}
       </div>
 
@@ -45,7 +45,7 @@
         {{combo-box
           value=filterPriority
           content=priorities
-          onChange=(mut filterPriority)
+          onChange=(action (mut filterPriority))
         }}
       </div>
 
@@ -54,7 +54,7 @@
         {{category-chooser
           none="review.filters.all_categories"
           value=filterCategoryId
-          onChange=(mut filterCategoryId)
+          onChange=(action (mut filterCategoryId))
         }}
       </div>
 
@@ -91,7 +91,7 @@
         {{combo-box
           value=filterSortOrder
           content=sortOrders
-          onChange=(mut filterSortOrder)
+          onChange=(action (mut filterSortOrder))
         }}
       </div>
     {{/if}}
diff --git a/app/assets/javascripts/discourse/app/templates/review-settings.hbs b/app/assets/javascripts/discourse/app/templates/review-settings.hbs
index 2fd2b55d5b2..599ae016020 100644
--- a/app/assets/javascripts/discourse/app/templates/review-settings.hbs
+++ b/app/assets/javascripts/discourse/app/templates/review-settings.hbs
@@ -8,7 +8,7 @@
         {{combo-box
           value=rst.reviewable_priority
           content=settings.reviewable_priorities
-          onChange=(mut rst.reviewable_priority)
+          onChange=(action (mut rst.reviewable_priority))
         }}
       </div>
     </div>
diff --git a/app/assets/javascripts/discourse/app/templates/user/notifications-index.hbs b/app/assets/javascripts/discourse/app/templates/user/notifications-index.hbs
index 646ba8497ae..14638f5f781 100644
--- a/app/assets/javascripts/discourse/app/templates/user/notifications-index.hbs
+++ b/app/assets/javascripts/discourse/app/templates/user/notifications-index.hbs
@@ -9,7 +9,7 @@
 {{/if}}
 
 <div class="user-notifications-filter-select-kit">
-  {{notifications-filter value=filter onChange=(fn (mut filter))}}
+  {{notifications-filter value=filter onChange=(action (mut filter))}}
 </div>
 
 {{#if hasFilteredNotifications}}
diff --git a/app/assets/javascripts/discourse/app/templates/users.hbs b/app/assets/javascripts/discourse/app/templates/users.hbs
index e751663968b..b406e63a751 100644
--- a/app/assets/javascripts/discourse/app/templates/users.hbs
+++ b/app/assets/javascripts/discourse/app/templates/users.hbs
@@ -5,7 +5,7 @@
         {{plugin-outlet name="users-top" connectorTagName="div" args=(hash model=model)}}
         <div class="directory-controls">
           <div class="period-controls">
-            {{period-chooser period=period onChange=(mut period) fullDay=false}}
+            {{period-chooser period=period onChange=(action (mut period)) fullDay=false}}
             {{#if lastUpdatedAt}}
               <div class="directory-last-updated">
                 {{i18n "directory.last_updated"}}
diff --git a/app/assets/javascripts/wizard/templates/components/invite-list.hbs b/app/assets/javascripts/wizard/templates/components/invite-list.hbs
index 301a1814f88..5c829fb9dc2 100644
--- a/app/assets/javascripts/wizard/templates/components/invite-list.hbs
+++ b/app/assets/javascripts/wizard/templates/components/invite-list.hbs
@@ -16,7 +16,7 @@
     value=inviteRole
     content=roles
     nameProperty="label"
-    onChange=(mut inviteRole)
+    onChange=(action (mut inviteRole))
   }}
 
   <button type="button" class="wizard-btn small add-user" {{action "addUser"}}>
diff --git a/app/assets/javascripts/wizard/templates/components/wizard-field-dropdown.hbs b/app/assets/javascripts/wizard/templates/components/wizard-field-dropdown.hbs
index 7a59b1fda84..e311b0183e9 100644
--- a/app/assets/javascripts/wizard/templates/components/wizard-field-dropdown.hbs
+++ b/app/assets/javascripts/wizard/templates/components/wizard-field-dropdown.hbs
@@ -5,5 +5,5 @@
   content=field.choices
   nameProperty="label"
   tabindex="9"
-  onChange=(fn (mut field.value))
+  onChange=(action (mut field.value))
 }}
diff --git a/plugins/discourse-local-dates/assets/javascripts/discourse/templates/components/discourse-local-dates-create-form.hbs b/plugins/discourse-local-dates/assets/javascripts/discourse/templates/components/discourse-local-dates-create-form.hbs
index d7bb47b65a7..196fb791c96 100644
--- a/plugins/discourse-local-dates/assets/javascripts/discourse/templates/components/discourse-local-dates-create-form.hbs
+++ b/plugins/discourse-local-dates/assets/javascripts/discourse/templates/components/discourse-local-dates-create-form.hbs
@@ -44,7 +44,7 @@
           {{timezone-input
             options=(hash icon="globe")
             value=timezone
-            onChange=(mut timezone)
+            onChange=(action (mut timezone))
           }}
         {{/unless}}
       </div>
@@ -74,7 +74,7 @@
         {{timezone-input
           value=timezone
           options=(hash icon="globe")
-          onChange=(mut timezone)
+          onChange=(action (mut timezone))
         }}
       {{/if}}
     </div>
@@ -92,7 +92,7 @@
                 content=recurringOptions
                 class="recurrence-input"
                 value=recurring
-                onChange=(mut recurring)
+                onChange=(action (mut recurring))
                 none="discourse_local_dates.create.form.recurring_none"}}
             </div>
           </div>
diff --git a/plugins/poll/assets/javascripts/discourse/templates/modal/poll-ui-builder.hbs b/plugins/poll/assets/javascripts/discourse/templates/modal/poll-ui-builder.hbs
index 2877959a465..3679c83037d 100644
--- a/plugins/poll/assets/javascripts/discourse/templates/modal/poll-ui-builder.hbs
+++ b/plugins/poll/assets/javascripts/discourse/templates/modal/poll-ui-builder.hbs
@@ -8,7 +8,7 @@
           value=pollType
           valueProperty="value"
           class="poll-type"
-          onChange=(mut pollType)
+          onChange=(action (mut pollType))
         }}
       </div>
 
@@ -19,7 +19,7 @@
           value=pollResult
           class="poll-result"
           valueProperty="value"
-          onChange=(mut pollResult)
+          onChange=(action (mut pollResult))
         }}
       </div>
 
@@ -28,7 +28,7 @@
         {{group-chooser
           content=siteGroups
           value=pollGroups
-          onChange=(mut pollGroups)
+          onChange=(action (mut pollGroups))
           labelProperty="name"
           valueProperty="name"}}
       </div>
@@ -41,7 +41,7 @@
             content=pollChartTypes
             value=chartType
             valueProperty="value"
-            onChange=(mut chartType)
+            onChange=(action (mut chartType))
           }}
         </div>
       {{/unless}}