44 files declare their use of AjaxResponse in Drupal 9

AddFormBase.php in core/modules/media_library/src/Form/AddFormBase.php

AjaxCssForm.php in core/modules/ckeditor/tests/modules/src/Form/AjaxCssForm.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

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

Simpletest mock module for Ajax forms testing.

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

Callbacks.php in core/modules/system/tests/modules/ajax_forms_test/src/Callbacks.php

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

EditorController.php in core/modules/editor/src/EditorController.php

EditorImageDialog.php in core/modules/editor/src/Form/EditorImageDialog.php

EditorLinkDialog.php in core/modules/editor/src/Form/EditorLinkDialog.php

EditorMediaDialog.php in core/modules/media/src/Form/EditorMediaDialog.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

JsAjaxTestForm.php in core/modules/system/tests/modules/js_ajax_test/src/Form/JsAjaxTestForm.php

LayoutRebuildTrait.php in core/modules/layout_builder/src/Controller/LayoutRebuildTrait.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

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

QuickEditController.php in core/modules/quickedit/src/QuickEditController.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