45 files declare their use of AjaxResponse

AddFormBase.php in core/modules/media_library/src/Form/AddFormBase.php
AjaxRenderer.php in core/lib/Drupal/Core/Render/MainContent/AjaxRenderer.php
AjaxResponseSubscriber.php in core/lib/Drupal/Core/EventSubscriber/AjaxResponseSubscriber.php
AjaxResponseTest.php in core/tests/Drupal/Tests/Core/Ajax/AjaxResponseTest.php
AjaxTestController.php in core/modules/system/tests/modules/ajax_test/src/Controller/AjaxTestController.php
AjaxTestDialogForm.php in core/modules/system/tests/modules/ajax_test/src/Form/AjaxTestDialogForm.php
AjaxTestFocusFirstForm.php in core/modules/system/tests/modules/ajax_test/src/Form/AjaxTestFocusFirstForm.php
AjaxTestForm.php in core/modules/system/tests/modules/ajax_test/src/Form/AjaxTestForm.php
AjaxTestFormPromise.php in core/modules/system/tests/modules/ajax_test/src/Form/AjaxTestFormPromise.php
AjaxTestImageEffect.php in core/modules/image/tests/modules/image_module_test/src/Plugin/ImageEffect/AjaxTestImageEffect.php
AjaxTestMessageCommandForm.php in core/modules/system/tests/modules/ajax_test/src/Form/AjaxTestMessageCommandForm.php
ajax_forms_test.module in core/modules/system/tests/modules/ajax_forms_test/ajax_forms_test.module
BigPipe.php in core/modules/big_pipe/src/Render/BigPipe.php
BigPipeResponseAttachmentsProcessorTest.php in core/modules/big_pipe/tests/src/Unit/Render/BigPipeResponseAttachmentsProcessorTest.php
BlockEntitySettingTrayForm.php in core/modules/settings_tray/src/Block/BlockEntitySettingTrayForm.php
CacheableAjaxResponse.php in core/lib/Drupal/Core/Cache/CacheableAjaxResponse.php
Callbacks.php in core/modules/system/tests/modules/ajax_forms_test/src/Callbacks.php
ckeditor5.module in core/modules/ckeditor5/ckeditor5.module
CommandsTest.php in core/tests/Drupal/KernelTests/Core/Ajax/CommandsTest.php
ContentModerationConfigureEntityTypesForm.php in core/modules/content_moderation/src/Form/ContentModerationConfigureEntityTypesForm.php
DialogRenderer.php in core/lib/Drupal/Core/Render/MainContent/DialogRenderer.php
DummyAjaxWidget.php in core/modules/image/tests/modules/image_module_test/src/Plugin/Field/FieldWidget/DummyAjaxWidget.php
EarlyRenderingControllerWrapperSubscriber.php in core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php
EarlyRenderingTestController.php in core/modules/system/tests/modules/early_rendering_controller_test/src/EarlyRenderingTestController.php
EntityDisplayFormBase.php in core/modules/field_ui/src/Form/EntityDisplayFormBase.php
FormAjaxResponseBuilder.php in core/lib/Drupal/Core/Form/FormAjaxResponseBuilder.php
FormAjaxResponseBuilderTest.php in core/tests/Drupal/Tests/Core/Form/FormAjaxResponseBuilderTest.php
FormAjaxSubscriber.php in core/lib/Drupal/Core/Form/EventSubscriber/FormAjaxSubscriber.php
LayoutRebuildTrait.php in core/modules/layout_builder/src/Controller/LayoutRebuildTrait.php
ListItemBase.php in core/modules/options/src/Plugin/Field/FieldType/ListItemBase.php
ManagedFile.php in core/modules/file/src/Element/ManagedFile.php
MediaLibraryEditorOpener.php in core/modules/media_library/src/MediaLibraryEditorOpener.php
MediaLibraryFieldWidgetOpener.php in core/modules/media_library/src/MediaLibraryFieldWidgetOpener.php
MediaLibrarySelectForm.php in core/modules/media_library/src/Plugin/views/field/MediaLibrarySelectForm.php
MediaLibraryWidget.php in core/modules/media_library/src/Plugin/Field/FieldWidget/MediaLibraryWidget.php
MediaTypeForm.php in core/modules/media/src/MediaTypeForm.php
ModalRenderer.php in core/lib/Drupal/Core/Render/MainContent/ModalRenderer.php
OffCanvasRenderer.php in core/lib/Drupal/Core/Render/MainContent/OffCanvasRenderer.php
ToolbarController.php in core/modules/toolbar/src/Controller/ToolbarController.php
ViewAjaxResponse.php in core/modules/views/src/Ajax/ViewAjaxResponse.php
ViewEditForm.php in core/modules/views_ui/src/ViewEditForm.php
ViewsFormBase.php in core/modules/views_ui/src/Form/Ajax/ViewsFormBase.php
ViewsUIController.php in core/modules/views_ui/src/Controller/ViewsUIController.php
WideModalRenderer.php in core/modules/system/tests/modules/dialog_renderer_test/src/Render/MainContent/WideModalRenderer.php
WidgetBase.php in core/lib/Drupal/Core/Field/WidgetBase.php

Buggy or inaccurate documentation? Please file an issue. Need support? Need help programming? Connect with the Drupal community.