From 5df48f5879409cf87fe0d0b189917f83108a27db Mon Sep 17 00:00:00 2001
From: Sergei Burkatskii <noreply@github.com>
Date: Tue, 23 Jun 2026 10:27:55 +0200
Subject: [PATCH 01/17] refactor: add simple return types

---
 .../js/__internal/scheduler/m_scheduler.ts    | 134 +++++++++---------
 1 file changed, 67 insertions(+), 67 deletions(-)

diff --git a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
index 5a02a006afb0..8893c5b264a5 100644
--- a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
+++ b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
@@ -244,7 +244,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this.timeZoneCalculatorInstance;
   }
 
-  private postponeDataSourceLoading(promise?: any) {
+  private postponeDataSourceLoading(promise?: any): void {
     this.postponedOperations.add('_reloadDataSource', this.reloadDataSource.bind(this), promise);
   }
 
@@ -613,7 +613,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
   }
 
-  private bringEditingModeToAppointments(editing) {
+  private bringEditingModeToAppointments(editing): void {
     const editingConfig: any = {
       allowDelete: editing.allowUpdating && editing.allowDeleting,
     };
@@ -628,7 +628,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.repaint();
   }
 
-  private isAgenda() {
+  private isAgenda(): boolean {
     return this.currentView.type === 'agenda';
   }
 
@@ -640,19 +640,19 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this.allowDragging() && !this._isAppointmentBeingUpdated(appointmentData);
   }
 
-  private allowResizing() {
+  private allowResizing(): boolean {
     return this.editing.allowResizing && !this.isAgenda();
   }
 
-  private allowAllDayResizing() {
+  private allowAllDayResizing(): boolean {
     return this.editing.allowResizing && this.supportAllDayResizing();
   }
 
-  private supportAllDayResizing() {
+  private supportAllDayResizing(): boolean {
     return this.currentView.type !== 'day' || this.currentView.intervalCount > 1;
   }
 
-  private isAllDayExpanded() {
+  private isAllDayExpanded(): boolean {
     return this.option('showAllDayPanel') && this._layoutManager.hasAllDayAppointments();
   }
 
@@ -712,7 +712,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return result.promise();
   }
 
-  _fireContentReadyAction(result?: any) {
+  _fireContentReadyAction(result?: any): void {
     // @ts-expect-error
     const contentReadyBase = super._fireContentReadyAction.bind(this);
     const fireContentReady = () => {
@@ -729,7 +729,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
   }
 
-  _dimensionChanged(value, isForce = false) {
+  _dimensionChanged(value, isForce = false): void {
     const isFixedHeight = typeof this.option('height') === 'number';
     const isFixedWidth = typeof this.option('width') === 'number';
 
@@ -764,22 +764,22 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.appointmentPopup.updatePopupFullScreenMode();
   }
 
-  _clean() {
+  _clean(): void {
     this.cleanPopup();
     // @ts-expect-error
     super._clean();
   }
 
-  private toggleSmallClass() {
+  private toggleSmallClass(): void {
     const { width } = getBoundingRect((this.$element() as any).get(0));
     (this.$element() as any).toggleClass(WIDGET_SMALL_CLASS, width < WIDGET_SMALL_WIDTH);
   }
 
-  private toggleAdaptiveClass() {
+  private toggleAdaptiveClass(): void {
     (this.$element() as any).toggleClass(WIDGET_ADAPTIVE_CLASS, this.option('adaptivityEnabled'));
   }
 
-  _visibilityChanged(visible) {
+  _visibilityChanged(visible): void {
     visible && this._dimensionChanged(null, true);
   }
 
@@ -787,13 +787,13 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return { paginate: false };
   }
 
-  private initAllDayPanel() {
+  private initAllDayPanel(): void {
     if (this.option('allDayPanelMode') === 'hidden') {
       this.option('showAllDayPanel', false);
     }
   }
 
-  _init() {
+  _init(): void {
     this.timeZonesPromise = timeZoneUtils.cacheTimeZones();
     this.initExpressions({
       startDateExpr: this.option('startDateExpr'),
@@ -852,12 +852,12 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     });
   }
 
-  createAppointmentDataSource() {
+  createAppointmentDataSource(): void {
     this.appointmentDataSource?.destroy();
     this.appointmentDataSource = new AppointmentDataSource(this._dataSource);
   }
 
-  updateAppointmentDataSource() {
+  updateAppointmentDataSource(): void {
     this.timeZoneCalculatorInstance = null;
 
     if (this.getWorkSpace()) {
@@ -865,14 +865,14 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
   }
 
-  private customizeDataSourceLoadOptions() {
+  private customizeDataSourceLoadOptions(): void {
     this._dataSource?.on('customizeStoreLoadOptions', ({ storeLoadOptions }) => {
       storeLoadOptions.startDate = this.getStartViewDate();
       storeLoadOptions.endDate = this.getEndViewDate();
     });
   }
 
-  _initTemplates() {
+  _initTemplates(): void {
     this.initAppointmentTemplate();
 
     this._templateManager.addDefaultTemplates({
@@ -884,7 +884,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   // TODO<Appointments>: delete this method when old impl is removed
-  private initAppointmentTemplate() {
+  private initAppointmentTemplate(): void {
     const { expr } = this._dataAccessors;
     const createGetter = (property) => compileGetter(`appointmentData.${property}`);
 
@@ -925,12 +925,12 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     });
   }
 
-  _renderContent() {
+  _renderContent(): void {
     // @ts-expect-error
     this._renderContentImpl();
   }
 
-  _dataSourceChangedHandler(result?: Appointment[]) {
+  _dataSourceChangedHandler(result?: Appointment[]): void {
     if (this.readyToRenderAppointments) {
       this.workSpaceRecalculation.done(() => {
         this._layoutManager.prepareAppointments(result);
@@ -952,7 +952,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return scrolling?.mode === 'virtual';
   }
 
-  private renderAppointments() {
+  private renderAppointments(): void {
     const workspace = this.getWorkSpace();
     this._layoutManager.filterAppointments();
 
@@ -971,7 +971,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
   }
 
-  private initExpressions(fields: IFieldExpr) {
+  private initExpressions(fields: IFieldExpr): void {
     this._dataAccessors = new AppointmentDataAccessor(
       fields,
       Boolean(config().forceIsoDateParsing),
@@ -979,11 +979,11 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     );
   }
 
-  private updateExpression(name: string, value: string) {
+  private updateExpression(name: string, value: string): void {
     this._dataAccessors.updateExpression(name, value);
   }
 
-  private initEditing() {
+  private initEditing(): void {
     const editing = this.option('editing');
 
     this.editing = {
@@ -1010,7 +1010,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     (this.$element() as any).toggleClass(WIDGET_READONLY_CLASS, isReadOnly);
   }
 
-  _dispose() {
+  _dispose(): void {
     this.resourceManager?.dispose();
     this.appointmentTooltip?.dispose();
     this.recurrenceDialog?.hide(RECURRENCE_EDITING_MODE.CANCEL);
@@ -1028,7 +1028,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     super._dispose();
   }
 
-  private initActions() {
+  private initActions(): void {
     this.actions = {
       onAppointmentAdding: this._createActionByOption(StoreEventNames.ADDING),
       onAppointmentAdded: this._createActionByOption(StoreEventNames.ADDED),
@@ -1053,9 +1053,9 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     });
   }
 
-  _renderFocusTarget() { return noop(); }
+  _renderFocusTarget(): void { return noop(); }
 
-  private updateA11yStatus() {
+  private updateA11yStatus(): void {
     const dateRange = this._workSpace.getDateRange();
     const indicatorTime = this.option('showCurrentTimeIndicator')
       ? getToday(this.option('indicatorTime') as Date, this.timeZoneCalculator)
@@ -1073,14 +1073,14 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.a11yStatus.text(label);
   }
 
-  private renderA11yStatus() {
+  private renderA11yStatus(): void {
     this.a11yStatus = createA11yStatusContainer();
     this.a11yStatus.prependTo(this.$element());
     // @ts-expect-error
     this.setAria({ role: 'application' });
   }
 
-  private initMarkupOnResourceLoaded() {
+  private initMarkupOnResourceLoaded(): void {
     if (!(this as any)._disposed) {
       this.initMarkupCore();
       this.reloadDataSource();
@@ -1161,7 +1161,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
   }
 
-  private createAppointmentPopupForm() {
+  private createAppointmentPopupForm(): void {
     if (this.appointmentForm) {
       this.appointmentForm.dispose();
     }
@@ -1171,7 +1171,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.appointmentPopup = this.createAppointmentPopup(this.appointmentForm);
   }
 
-  private renderMainContainer() {
+  private renderMainContainer(): void {
     this.mainContainer = $('<div>').addClass('dx-scheduler-container');
     this.$draggableContainer = $('<div>')
       .addClass('dx-scheduler-draggable-container')
@@ -1290,7 +1290,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     });
   }
 
-  checkAndDeleteAppointment(appointment, targetedAppointment) {
+  checkAndDeleteAppointment(appointment, targetedAppointment): void {
     const targetedAdapter = new AppointmentAdapter(
       targetedAppointment,
       this._dataAccessors,
@@ -1316,14 +1316,14 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     };
   }
 
-  isAppointmentInAllDayPanel(appointmentData) {
+  isAppointmentInAllDayPanel(appointmentData): boolean {
     const workSpace = this._workSpace;
     const itTakesAllDay = this.appointmentTakesAllDay(appointmentData);
 
     return itTakesAllDay && workSpace.supportAllDayRow() && workSpace.option('showAllDayPanel');
   }
 
-  private initMarkupCore() {
+  private initMarkupCore(): void {
     this.readyToRenderAppointments = hasWindow();
 
     this._workSpace && this.cleanWorkspace();
@@ -1345,18 +1345,18 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.updateA11yStatus();
   }
 
-  private isDataSourceLoaded() {
+  private isDataSourceLoaded(): boolean {
     return this._dataSource?.isLoaded();
   }
 
-  _render() {
+  _render(): void {
     this.getWorkSpace()?.updateHeaderEmptyCellWidth();
 
     // @ts-expect-error
     super._render();
   }
 
-  private renderHeader() {
+  private renderHeader(): void {
     const toolbarOptions = this.option('toolbar');
     const isHeaderShown = Boolean(
       toolbarOptions.visible ?? toolbarOptions.items?.length,
@@ -1431,7 +1431,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return config;
   }
 
-  private renderWorkSpace() {
+  private renderWorkSpace(): void {
     const currentViewOptions = this.currentView;
     if (!currentViewOptions) {
       return;
@@ -1482,7 +1482,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this._workSpace.getWorkArea().append(this._appointments.$element());
   }
 
-  private recalculateWorkspace() {
+  private recalculateWorkspace(): void {
     // @ts-expect-error
     this.workSpaceRecalculation = new Deferred();
     triggerResizeEvent(this._workSpace.$element());
@@ -1587,7 +1587,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return result;
   }
 
-  private waitAsyncTemplate(callback) {
+  private waitAsyncTemplate(callback): void {
     if (this._options.silent('templatesRenderAsynchronously')) {
       const timer = setTimeout(() => {
         callback();
@@ -1637,7 +1637,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
   }
 
-  private cleanWorkspace() {
+  private cleanWorkspace(): void {
     this._appointments.$element().detach();
     this._workSpace._dispose();
     this._workSpace.$element().remove();
@@ -1661,7 +1661,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this.header;
   }
 
-  private cleanPopup() {
+  private cleanPopup(): void {
     this.appointmentPopup?.dispose();
   }
 
@@ -1704,7 +1704,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     dragEvent?: any,
     recurrenceEditMode?: any,
     onCancel?: () => void,
-  ) {
+  ): void {
     const recurrenceRule = this._dataAccessors.get('recurrenceRule', rawAppointment);
 
     if (!validateRRule(recurrenceRule) || !this.editing.allowUpdating) {
@@ -1748,7 +1748,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
   }
 
-  private excludeAppointmentFromSeries(rawAppointment, newRawAppointment, exceptionDate, isDeleted, isPopupEditing, dragEvent) {
+  private excludeAppointmentFromSeries(rawAppointment, newRawAppointment, exceptionDate, isDeleted, isPopupEditing, dragEvent): void {
     const appointment = excludeFromRecurrence(
       rawAppointment,
       exceptionDate,
@@ -1787,7 +1787,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
   }
 
-  private createRecurrenceException(appointment, exceptionDate) {
+  private createRecurrenceException(appointment, exceptionDate): string {
     const result: any[] = [];
 
     if (appointment.recurrenceException) {
@@ -1798,7 +1798,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return result.join();
   }
 
-  private getSerializedDate(date, startDate, isAllDay) {
+  private getSerializedDate(date, startDate, isAllDay): string {
     isAllDay && date.setHours(
       startDate.getHours(),
       startDate.getMinutes(),
@@ -1934,7 +1934,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     );
   }
 
-  subscribe(subject, action) {
+  subscribe(subject, action): void {
     this.subscribes[subject] = subscribes[subject] = action;
   }
 
@@ -2038,13 +2038,13 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return deferred.promise();
   }
 
-  private expandAllDayPanel(appointment) {
+  private expandAllDayPanel(appointment): void {
     if (!this.isAllDayExpanded() && this.appointmentTakesAllDay(appointment)) {
       this.updateOption('workSpace', 'allDayExpanded', true);
     }
   }
 
-  private onDataPromiseCompleted(handlerName, storeAppointment, appointment?: any) {
+  private onDataPromiseCompleted(handlerName, storeAppointment, appointment?: any): void {
     const args: any = { appointmentData: appointment || storeAppointment };
 
     if (storeAppointment instanceof Error) {
@@ -2069,7 +2069,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this.actions;
   }
 
-  appointmentTakesAllDay(rawAppointment) {
+  appointmentTakesAllDay(rawAppointment): boolean {
     const appointment = new AppointmentAdapter(
       rawAppointment,
       this._dataAccessors,
@@ -2081,7 +2081,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     );
   }
 
-  dayHasAppointment(day, rawAppointment, trimTime) {
+  dayHasAppointment(day, rawAppointment, trimTime): boolean {
     const getConvertedToTimeZone = (date) => this.timeZoneCalculator.createDate(date, 'toGrid');
 
     const appointment = new AppointmentAdapter(
@@ -2120,7 +2120,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this._workSpace.getEndViewDate();
   }
 
-  showAddAppointmentPopup(cellData, cellGroups) {
+  showAddAppointmentPopup(cellData, cellGroups): void {
     const appointmentAdapter = new AppointmentAdapter({}, this._dataAccessors);
 
     appointmentAdapter.allDay = Boolean(cellData.allDay);
@@ -2131,7 +2131,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.showAppointmentPopup(resultAppointment, true);
   }
 
-  showAppointmentPopup(rawAppointment?: any, createNewAppointment?: boolean, rawTargetedAppointment?: any) {
+  showAppointmentPopup(rawAppointment?: any, createNewAppointment?: boolean, rawTargetedAppointment?: any): void {
     const newRawTargetedAppointment = { ...rawTargetedAppointment };
     if (newRawTargetedAppointment) {
       delete newRawTargetedAppointment.displayStartDate;
@@ -2189,7 +2189,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return result;
   }
 
-  hideAppointmentPopup(saveChanges?: any) {
+  hideAppointmentPopup(saveChanges?: any): void {
     if (this.appointmentPopup?.visible) {
       saveChanges && this.appointmentPopup.saveChangesAsync();
       this.appointmentPopup.hide();
@@ -2201,7 +2201,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     appointment: SafeAppointment,
     element: dxElementWrapper,
     targetedAppointment?: SafeAppointment,
-  ) {
+  ): void {
     if (appointment) {
       const settings: any = utils.dataAccessors.getAppointmentSettings(element);
       const appointmentConfig = {
@@ -2224,7 +2224,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     target: dxElementWrapper,
     data: AppointmentTooltipItem[],
     options?: AppointmentTooltipExtraOptions,
-  ) {
+  ): void {
     const arg: Omit<AppointmentTooltipShowingEvent, 'component' | 'element'> = {
       cancel: false,
       appointments: data.map((item) => ({
@@ -2249,7 +2249,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
   }
 
-  hideAppointmentTooltip() {
+  hideAppointmentTooltip(): void {
     this.appointmentTooltip?.hide();
   }
 
@@ -2257,7 +2257,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     date: Date,
     groupValuesOrOptions?: ScrollToGroupValuesOrOptions,
     allDay?: boolean | undefined,
-  ) {
+  ): void {
     let groupValues;
     let allDayValue;
     let align: 'start' | 'center' = 'center';
@@ -2283,7 +2283,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       && ('alignInView' in options || 'allDay' in options || 'group' in options);
   }
 
-  private isHorizontalVirtualScrolling() {
+  private isHorizontalVirtualScrolling(): boolean {
     const scrolling = this.option('scrolling');
     const { orientation, mode } = scrolling;
     const isVirtualScrolling = mode === 'virtual';
@@ -2327,7 +2327,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this.updateAppointmentCore(target, appointment);
   }
 
-  deleteAppointment(rawAppointment) {
+  deleteAppointment(rawAppointment): void {
     const deletingOptions = this.fireOnAppointmentDeleting(rawAppointment);
     this.processDeleteAppointment(rawAppointment, deletingOptions);
   }
@@ -2344,7 +2344,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return deletingOptions;
   }
 
-  processDeleteAppointment(rawAppointment, deletingOptions) {
+  processDeleteAppointment(rawAppointment, deletingOptions): void {
     this.processActionResult(deletingOptions, function (canceled) {
       if (!canceled) {
         this.appointmentDataSource
@@ -2362,7 +2362,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     appointment,
     date: Date | string,
     recurrenceEditMode,
-  ) {
+  ): void {
     if (typeof date === 'string') {
       date = new Date(date);
     }
@@ -2383,7 +2383,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     );
   }
 
-  focus() {
+  focus(): void {
     if (this.editAppointmentData) {
       this._appointments.focus();
     } else {
@@ -2401,7 +2401,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       : dateLocalization.firstDayOfWeekIndex() as DayOfWeek;
   }
 
-  private validateKeyFieldIfAgendaExist() {
+  private validateKeyFieldIfAgendaExist(): void {
     if (!this.appointmentDataSource.isDataSourceInit) {
       return;
     }

From 5e91cc3843cb87662979bc63705d95f4e1102fe6 Mon Sep 17 00:00:00 2001
From: Sergei Burkatskii <noreply@github.com>
Date: Tue, 23 Jun 2026 10:29:55 +0200
Subject: [PATCH 02/17] refactor: enhance type safety for time zone calculator
 in scheduler

---
 .../devextreme/js/__internal/scheduler/m_scheduler.ts     | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
index 8893c5b264a5..5e7aed7a9916 100644
--- a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
+++ b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
@@ -52,7 +52,7 @@ import { CompactAppointmentsHelper } from './m_compact_appointments_helper';
 import type { SubscribeKey, SubscribeMethods } from './m_subscribes';
 import subscribes from './m_subscribes';
 import { combineRemoteFilter } from './r1/filterting/remote';
-import { createTimeZoneCalculator } from './r1/timezone_calculator/index';
+import { createTimeZoneCalculator, type TimeZoneCalculator } from './r1/timezone_calculator/index';
 import {
   excludeFromRecurrence,
   getToday,
@@ -165,7 +165,7 @@ const RECURRENCE_EDITING_MODE = {
 class Scheduler extends SchedulerOptionsBaseWidget {
   // NOTE: Do not initialize variables here, because `_initMarkup` function runs before constructor,
   // and initialization in constructor will erase the data
-  private timeZoneCalculatorInstance!: any;
+  private timeZoneCalculatorInstance: TimeZoneCalculator | null = null;
 
   postponedOperations: any;
 
@@ -236,7 +236,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
   private timeZonesPromise!: Promise<TimezoneLabel[]>;
 
-  get timeZoneCalculator() {
+  get timeZoneCalculator(): TimeZoneCalculator {
     if (!this.timeZoneCalculatorInstance) {
       this.timeZoneCalculatorInstance = createTimeZoneCalculator(this.option('timeZone'));
     }
@@ -1206,7 +1206,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
       getEditingConfig: () => this.editing,
 
-      getTimeZoneCalculator: () => this.timeZoneCalculator,
+      getTimeZoneCalculator: (): TimeZoneCalculator => this.timeZoneCalculator,
       getDataAccessors: () => this._dataAccessors,
       getAppointmentFormOpening: () => this.actions.onAppointmentFormOpening,
       processActionResult: (arg, canceled) => this.processActionResult(arg, canceled),

From 20a1eb3f2437776b28b7697b86e1739daea13428 Mon Sep 17 00:00:00 2001
From: Sergei Burkatskii <noreply@github.com>
Date: Tue, 23 Jun 2026 10:31:38 +0200
Subject: [PATCH 03/17] refactor: improve type annotations for scheduler
 methods

---
 .../js/__internal/scheduler/m_scheduler.ts    | 21 ++++++++++---------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
index 5e7aed7a9916..ca4061f3dd27 100644
--- a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
+++ b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
@@ -26,6 +26,7 @@ import {
   isPromise,
 } from '@js/core/utils/type';
 import { hasWindow } from '@js/core/utils/window';
+import type { DataSourceOptions } from '@js/data/data_source';
 import DataHelperMixin from '@js/data_helper';
 import { custom as customDialog } from '@js/ui/dialog';
 import type {
@@ -783,7 +784,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     visible && this._dimensionChanged(null, true);
   }
 
-  _dataSourceOptions() {
+  _dataSourceOptions(): DataSourceOptions {
     return { paginate: false };
   }
 
@@ -1120,7 +1121,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         getResourceManager: () => this.resourceManager,
         getAppointmentDataSource: () => this.appointmentDataSource,
         getDataAccessor: () => this._dataAccessors,
-        getStartViewDate: () => this.getStartViewDate(),
+        getStartViewDate: (): Date => this.getStartViewDate()!,
         getSortedItems: () => this._layoutManager.sortedItems,
 
         isVirtualScrolling: () => this.isVirtualScrolling(),
@@ -1180,7 +1181,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.$element().append(this.mainContainer);
   }
 
-  createAppointmentForm() {
+  createAppointmentForm(): AppointmentForm {
     const config: AppointmentFormConfig = {
       dataAccessors: this._dataAccessors,
       editing: this.editing,
@@ -1195,7 +1196,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return new AppointmentForm(config);
   }
 
-  createAppointmentPopup(form) {
+  createAppointmentPopup(form: AppointmentForm): AppointmentPopup {
     const scheduler = {
       getElement: () => this.$element(),
       // @ts-expect-error
@@ -1307,7 +1308,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     );
   }
 
-  private getExtraAppointmentTooltipOptions() {
+  private getExtraAppointmentTooltipOptions(): AppointmentTooltipExtraOptions {
     return {
       rtlEnabled: this.option('rtlEnabled'),
       focusStateEnabled: this.option('focusStateEnabled'),
@@ -1379,7 +1380,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       min: this.getViewOption('min'),
       max: this.getViewOption('max'),
       indicatorTime: this.option('indicatorTime'),
-      startViewDate: this.getStartViewDate(),
+      startViewDate: this.getStartViewDate()!,
       tabIndex: this.option('tabIndex'),
       focusStateEnabled: this.option('focusStateEnabled'),
       useDropDownViewSwitcher: this.option('useDropDownViewSwitcher'),
@@ -1657,7 +1658,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this._workSpace;
   }
 
-  getHeader() {
+  getHeader(): SchedulerHeader | undefined {
     return this.header;
   }
 
@@ -2061,7 +2062,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this._appointments;
   }
 
-  getLayoutManager() {
+  getLayoutManager(): AppointmentLayoutManager {
     return this._layoutManager;
   }
 
@@ -2112,11 +2113,11 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return startDateTimeStamp <= dayTimeStamp && dayTimeStamp <= endDateTimeStamp;
   }
 
-  getStartViewDate() {
+  getStartViewDate(): Date | undefined {
     return this._workSpace?.getStartViewDate();
   }
 
-  getEndViewDate() {
+  getEndViewDate(): Date {
     return this._workSpace.getEndViewDate();
   }
 

From 52ebedc4fca1ad1b83dfdbc110a58d77deaac15c Mon Sep 17 00:00:00 2001
From: Sergei Burkatskii <noreply@github.com>
Date: Tue, 23 Jun 2026 11:51:32 +0200
Subject: [PATCH 04/17] refactor:  add type to workspace in scheduler

---
 .../js/__internal/scheduler/m_scheduler.ts    | 45 ++++++++++++-------
 .../scheduler/workspaces/work_space.ts        |  2 +-
 2 files changed, 30 insertions(+), 17 deletions(-)

diff --git a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
index ca4061f3dd27..014f6a75653f 100644
--- a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
+++ b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
@@ -8,6 +8,7 @@ import type { dxElementWrapper } from '@js/core/renderer';
 import $ from '@js/core/renderer';
 import { BindableTemplate } from '@js/core/templates/bindable_template';
 import { EmptyTemplate } from '@js/core/templates/empty_template';
+import type { FunctionTemplate } from '@js/core/templates/function_template';
 import Callbacks from '@js/core/utils/callbacks';
 import { noop } from '@js/core/utils/common';
 import { compileGetter } from '@js/core/utils/data';
@@ -35,6 +36,7 @@ import type {
 import errors from '@js/ui/widget/ui.errors';
 import { dateUtilsTs } from '@ts/core/utils/date';
 import type { OptionChanged } from '@ts/core/widget/types';
+import type Scrollable from '@ts/ui/scroll_view/scrollable';
 
 import { createA11yStatusContainer } from './a11y_status/a11y_status_render';
 import { getA11yStatusText } from './a11y_status/a11y_status_text';
@@ -49,6 +51,7 @@ import NotifyScheduler from './base/widget_notify_scheduler';
 import { SchedulerHeader } from './header/header';
 import type { HeaderOptions } from './header/types';
 import { hide as hideLoading, show as showLoading } from './loading';
+import type AppointmentDragBehavior from './m_appointment_drag_behavior';
 import { CompactAppointmentsHelper } from './m_compact_appointments_helper';
 import type { SubscribeKey, SubscribeMethods } from './m_subscribes';
 import subscribes from './m_subscribes';
@@ -91,6 +94,8 @@ import SchedulerAgenda from './workspaces/agenda';
 import SchedulerTimelineDay from './workspaces/timeline_day';
 import SchedulerTimelineMonth from './workspaces/timeline_month';
 import SchedulerTimelineWeek from './workspaces/timeline_week';
+import type SchedulerWorkSpace from './workspaces/work_space';
+import type { DroppableCellData } from './workspaces/work_space';
 import SchedulerWorkSpaceDay from './workspaces/work_space_day';
 import SchedulerWorkSpaceMonth from './workspaces/work_space_month';
 import SchedulerWorkSpaceWeek from './workspaces/work_space_week';
@@ -173,7 +178,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   private a11yStatus!: dxElementWrapper;
 
   // TODO: used externally in m_appointment_drag_behavior.ts, m_subscribes.ts, workspaces/work_space.ts
-  _workSpace: any;
+  _workSpace!: SchedulerWorkSpace;
 
   private header?: SchedulerHeader;
 
@@ -957,7 +962,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     const workspace = this.getWorkSpace();
     this._layoutManager.filterAppointments();
 
-    workspace.option('allDayExpanded', this.isAllDayExpanded());
+    workspace?.option('allDayExpanded', this.isAllDayExpanded());
 
     // @ts-expect-error
     const viewModel: AppointmentViewModelPlain[] = this._isVisible()
@@ -968,7 +973,8 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.appointmentDataSource.cleanState();
 
     if (this.isAgenda()) {
-      this._workSpace.renderAgendaLayout(viewModel);
+      // @ts-expect-error renderAgendaLayout exists only on agenda workspace
+      this._workSpace.renderAgendaLayout?.(viewModel);
     }
   }
 
@@ -1321,7 +1327,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     const workSpace = this._workSpace;
     const itTakesAllDay = this.appointmentTakesAllDay(appointmentData);
 
-    return itTakesAllDay && workSpace.supportAllDayRow() && workSpace.option('showAllDayPanel');
+    return itTakesAllDay && workSpace.supportAllDayRow() && Boolean(workSpace.option('showAllDayPanel'));
   }
 
   private initMarkupCore(): void {
@@ -1422,6 +1428,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       getResizableStep: () => (this._workSpace ? this._workSpace.positionHelper.getResizableStep() : 0),
       getDOMElementsMetaData: () => this._workSpace?.getDOMElementsMetaData(),
       getViewDataProvider: () => this._workSpace?.viewDataProvider,
+      // @ts-expect-error protected method
       isVerticalGroupedWorkSpace: () => this._workSpace.isVerticalGroupedWorkSpace(),
       isDateAndTimeView: () => isDateAndTimeView(this._workSpace.type),
       onContentReady: () => {
@@ -1446,6 +1453,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
     this.recalculateWorkspace();
     if (currentViewOptions.startDate) {
+      // @ts-expect-error protected method
       this.updateOption('header', 'currentDate', this._workSpace.getHeaderDate());
     }
   }
@@ -1468,8 +1476,11 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this._workSpace = this._createComponent($workSpace, workSpaceComponent, workSpaceConfig);
 
     if (!this.option('_newAppointments')) {
-      this.allowDragging() && this._workSpace.initDragBehavior(this, this.all);
+      if (this.allowDragging()) {
+        this._workSpace.initDragBehavior(this);
+      }
     }
+    // @ts-expect-error protected method
     this._workSpace.attachTablesEvents();
     this._workSpace.getWorkArea().append(this._appointments.$element());
   }
@@ -1488,6 +1499,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.workSpaceRecalculation = new Deferred();
     triggerResizeEvent(this._workSpace.$element());
     this.waitAsyncTemplate(() => {
+      // @ts-expect-error protected method
       this._workSpace.renderCurrentDateTimeLineAndShader();
     });
   }
@@ -1600,7 +1612,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
   }
 
-  getAppointmentTemplate(optionName) {
+  getAppointmentTemplate(optionName: string): FunctionTemplate {
     if (this.currentView?.[optionName]) {
       return this._getTemplate(this.currentView[optionName]);
     }
@@ -1620,7 +1632,8 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   private refreshWorkSpace(): void {
     this.cleanWorkspace();
 
-    delete this._workSpace;
+    // @ts-expect-error
+    this._workSpace = undefined;
 
     this.renderWorkSpace();
 
@@ -1646,15 +1659,15 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.option('selectedCellData', []);
   }
 
-  getWorkSpaceScrollable() {
+  getWorkSpaceScrollable(): Scrollable {
     return this._workSpace.getScrollable();
   }
 
-  getWorkSpaceScrollableContainer() {
+  getWorkSpaceScrollableContainer(): dxElementWrapper {
     return this._workSpace.getScrollableContainer();
   }
 
-  getWorkSpace() {
+  getWorkSpace(): SchedulerWorkSpace | undefined {
     return this._workSpace;
   }
 
@@ -1836,7 +1849,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this.recurrenceDialog.show();
   }
 
-  getUpdatedData(rawAppointment, $cell?) {
+  getUpdatedData(rawAppointment: Appointment, $cell?: dxElementWrapper): SafeAppointment {
     const viewOffset = this.getViewOffsetMs();
 
     const getConvertedFromGrid = (date: any): Date | undefined => {
@@ -1952,7 +1965,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return callback.call(this, ...args);
   }
 
-  getTargetCellData() {
+  getTargetCellData(): DroppableCellData {
     return this._workSpace.getDataByDroppableCell();
   }
 
@@ -2058,7 +2071,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this._fireContentReadyAction();
   }
 
-  getAppointmentsInstance() {
+  getAppointmentsInstance(): Appointments | AppointmentCollection {
     return this._appointments;
   }
 
@@ -2177,8 +2190,8 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
   }
 
-  createPopupAppointment() {
-    const result: any = {};
+  createPopupAppointment(): SafeAppointment {
+    const result: SafeAppointment = {};
     const toMs = dateUtils.dateToMilliseconds;
 
     const startDate = new Date(this.option('currentDate'));
@@ -2416,7 +2429,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   // TODO: used externally in m_appointment_drag_behavior.ts
-  _getDragBehavior() {
+  _getDragBehavior(): AppointmentDragBehavior | null {
     return this._workSpace.dragBehavior;
   }
 
diff --git a/packages/devextreme/js/__internal/scheduler/workspaces/work_space.ts b/packages/devextreme/js/__internal/scheduler/workspaces/work_space.ts
index b6f56ca6b301..6e839a9a16fe 100644
--- a/packages/devextreme/js/__internal/scheduler/workspaces/work_space.ts
+++ b/packages/devextreme/js/__internal/scheduler/workspaces/work_space.ts
@@ -266,7 +266,7 @@ interface WorkspaceOptionActionMap {
 
 type WorkspaceCoordinates = Coordinates & { groupIndex?: number };
 
-type DroppableCellData = Pick<ViewCellData, 'startDate' | 'endDate' | 'allDay' | 'groups'>;
+export type DroppableCellData = Pick<ViewCellData, 'startDate' | 'endDate' | 'allDay' | 'groups'>;
 
 export interface WorkspaceOptionsInternal extends WidgetProperties<SchedulerWorkSpace> {
   newAppointments: boolean;

From 13a4d2924cf8c7098c5f8494df8bfc41bdae086e Mon Sep 17 00:00:00 2001
From: Sergei Burkatskii <noreply@github.com>
Date: Tue, 23 Jun 2026 11:52:14 +0200
Subject: [PATCH 05/17] refactor: improve type definitions for deferred

---
 .../js/__internal/scheduler/m_scheduler.ts    | 73 ++++++++++++-------
 1 file changed, 45 insertions(+), 28 deletions(-)

diff --git a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
index 014f6a75653f..049279f3712a 100644
--- a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
+++ b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
@@ -14,7 +14,8 @@ import { noop } from '@js/core/utils/common';
 import { compileGetter } from '@js/core/utils/data';
 import dateUtils from '@js/core/utils/date';
 import dateSerialization from '@js/core/utils/date_serialization';
-// @ts-expect-error
+import type { DeferredObj } from '@js/core/utils/deferred';
+// @ts-expect-error untyped deferred module re-export
 import { Deferred, fromPromise, when } from '@js/core/utils/deferred';
 import { extend } from '@js/core/utils/extend';
 import { getBoundingRect } from '@js/core/utils/position';
@@ -168,6 +169,20 @@ const RECURRENCE_EDITING_MODE = {
   CANCEL: 'cancel',
 };
 
+type SchedulerActionCancel = boolean | PromiseLike<boolean> | DeferredObj<boolean | undefined>;
+
+type SchedulerActionOptions = {
+  cancel: SchedulerActionCancel;
+} & Record<string, unknown>;
+
+type ProcessActionCallback = (
+  canceled: boolean,
+) => unknown;
+
+interface SchedulerDragEvent {
+  cancel: DeferredObj<boolean>;
+}
+
 class Scheduler extends SchedulerOptionsBaseWidget {
   // NOTE: Do not initialize variables here, because `_initMarkup` function runs before constructor,
   // and initialization in constructor will erase the data
@@ -254,15 +269,14 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.postponedOperations.add('_reloadDataSource', this.reloadDataSource.bind(this), promise);
   }
 
-  private postponeResourceLoading(forceReload = false) {
+  private postponeResourceLoading(forceReload = false): DeferredObj<void> {
     const whenLoaded = this.postponedOperations.add('loadResources', () => {
       const groups = this.getViewOption('groups');
 
       return fromPromise(this.resourceManager.loadGroupResources(groups, forceReload));
     });
 
-    // @ts-expect-error
-    const resolveCallbacks = new Deferred();
+    const resolveCallbacks: DeferredObj<void> = Deferred();
 
     whenLoaded.done(() => {
       resolveCallbacks.resolve();
@@ -270,7 +284,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
     this.postponeDataSourceLoading(whenLoaded);
 
-    return resolveCallbacks.promise();
+    return resolveCallbacks;
   }
 
   _optionChanged(args: OptionChanged<SafeSchedulerOptions>): void {
@@ -689,9 +703,8 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     dataSource.filter(filter);
   }
 
-  private reloadDataSource() {
-    // @ts-expect-error
-    const result = new Deferred();
+  private reloadDataSource(): Promise<void> {
+    const result: DeferredObj<void> = Deferred();
 
     if (this._dataSource) {
       this._dataSource.load().done(() => {
@@ -718,7 +731,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return result.promise();
   }
 
-  _fireContentReadyAction(result?: any): void {
+  _fireContentReadyAction(result?: DeferredObj<void>): void {
     // @ts-expect-error
     const contentReadyBase = super._fireContentReadyAction.bind(this);
     const fireContentReady = () => {
@@ -1697,7 +1710,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
           this.updateAppointmentCore(
             appointmentData,
             newAppointmentData,
-          ).always(resolve);
+          ).finally(resolve);
         },
         false,
         undefined,
@@ -1823,7 +1836,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return dateSerialization.serializeDate(date, UTC_FULL_DATE_FORMAT);
   }
 
-  private showRecurrenceChangeConfirm(isDeleted) {
+  private showRecurrenceChangeConfirm(isDeleted: boolean): DeferredObj<string> {
     const title = messageLocalization.format(isDeleted ? 'dxScheduler-confirmRecurrenceDeleteTitle' : 'dxScheduler-confirmRecurrenceEditTitle');
     const message = messageLocalization.format(isDeleted ? 'dxScheduler-confirmRecurrenceDeleteMessage' : 'dxScheduler-confirmRecurrenceEditMessage');
     const seriesText = messageLocalization.format(isDeleted ? 'dxScheduler-confirmRecurrenceDeleteSeries' : 'dxScheduler-confirmRecurrenceEditSeries');
@@ -1969,7 +1982,12 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this._workSpace.getDataByDroppableCell();
   }
 
-  updateAppointmentCore(target, rawAppointment, onUpdatePrevented?: any, dragEvent?: any) {
+  updateAppointmentCore(
+    target: SafeAppointment,
+    rawAppointment: SafeAppointment,
+    onUpdatePrevented?: () => void,
+    dragEvent?: SchedulerDragEvent,
+  ): Promise<void> {
     const updatingOptions = {
       newData: rawAppointment,
       oldData: extend({}, target),
@@ -1989,8 +2007,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.actions[StoreEventNames.UPDATING](updatingOptions);
 
     if (dragEvent && !isDeferred(dragEvent.cancel)) {
-      // @ts-expect-error
-      dragEvent.cancel = new Deferred();
+      dragEvent.cancel = Deferred<boolean>();
     }
 
     if (isPromise(updatingOptions.cancel) && (dragEvent || this.option('_newAppointments'))) {
@@ -1998,8 +2015,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
 
     return this.processActionResult(updatingOptions, function (canceled) {
-      // @ts-expect-error
-      let deferred = new Deferred();
+      let deferred: DeferredObj<void> = Deferred();
 
       if (!canceled) {
         this.expandAllDayPanel(rawAppointment);
@@ -2030,23 +2046,25 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     });
   }
 
-  private processActionResult(actionOptions, callback) {
-    // @ts-expect-error
-    const deferred = new Deferred();
-    const resolveCallback = (callbackResult) => {
+  private processActionResult(
+    actionOptions: SchedulerActionOptions,
+    callback: ProcessActionCallback,
+  ): Promise<void> {
+    const deferred: DeferredObj<void> = Deferred();
+    const resolveCallback = (callbackResult: unknown): void => {
       when(fromPromise(callbackResult))
-        .always(deferred.resolve);
+        .always(() => { deferred.resolve(); });
     };
 
     if (isPromise(actionOptions.cancel)) {
       when(fromPromise(actionOptions.cancel)).always((cancel) => {
         if (!isDefined(cancel)) {
-          cancel = actionOptions.cancel.state() === 'rejected';
+          cancel = (actionOptions.cancel as DeferredObj<boolean>).state() === 'rejected';
         }
         resolveCallback(callback.call(this, cancel));
       });
     } else {
-      resolveCallback(callback.call(this, actionOptions.cancel));
+      resolveCallback(callback.call(this, actionOptions.cancel as boolean));
     }
 
     return deferred.promise();
@@ -2254,7 +2272,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     if (this.appointmentTooltip.isShownForTarget(target)) {
       this.hideAppointmentTooltip();
     } else {
-      this.processActionResult(arg, (canceled) => {
+      this.processActionResult({ ...arg, cancel: arg.cancel ?? false }, (canceled) => {
         !canceled && this.appointmentTooltip.show(target, data, {
           ...this.getExtraAppointmentTooltipOptions(),
           ...options,
@@ -2306,7 +2324,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       && (orientation === 'horizontal' || orientation === 'both');
   }
 
-  addAppointment(rawAppointment) {
+  addAppointment(rawAppointment: SafeAppointment): Promise<void> {
     // NOTE: mutation of raw appointment
     const appointment = new AppointmentAdapter(
       rawAppointment,
@@ -2325,8 +2343,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
     return this.processActionResult(addingOptions, (canceled) => {
       if (canceled) {
-        // @ts-expect-error
-        return new Deferred().resolve();
+        return Deferred().resolve().promise();
       }
 
       this.expandAllDayPanel(serializedAppointment);
@@ -2337,7 +2354,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     });
   }
 
-  updateAppointment(target, appointment) {
+  updateAppointment(target: SafeAppointment, appointment: SafeAppointment): Promise<void> {
     return this.updateAppointmentCore(target, appointment);
   }
 

From 8b179639b975d7280d1e98c0af478f1fd799088c Mon Sep 17 00:00:00 2001
From: Sergei Burkatskii <noreply@github.com>
Date: Tue, 23 Jun 2026 11:55:48 +0200
Subject: [PATCH 06/17] refactor: add type for actions

---
 .../js/__internal/scheduler/m_scheduler.ts    | 87 +++++++++++++++----
 1 file changed, 70 insertions(+), 17 deletions(-)

diff --git a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
index 049279f3712a..b175b983bcd2 100644
--- a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
+++ b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
@@ -32,7 +32,18 @@ import type { DataSourceOptions } from '@js/data/data_source';
 import DataHelperMixin from '@js/data_helper';
 import { custom as customDialog } from '@js/ui/dialog';
 import type {
-  Appointment, AppointmentTooltipShowingEvent, DayOfWeek, Occurrence,
+  Appointment,
+  AppointmentAddingEvent,
+  AppointmentClickEvent,
+  AppointmentContextMenuEvent,
+  AppointmentDblClickEvent,
+  AppointmentFormOpeningEvent,
+  AppointmentRenderedEvent,
+  AppointmentTooltipShowingEvent,
+  AppointmentUpdatingEvent,
+  DayOfWeek,
+  Occurrence,
+  SelectionEndEvent,
 } from '@js/ui/scheduler';
 import errors from '@js/ui/widget/ui.errors';
 import { dateUtilsTs } from '@ts/core/utils/date';
@@ -183,6 +194,40 @@ interface SchedulerDragEvent {
   cancel: DeferredObj<boolean>;
 }
 
+type SchedulerEventArgs<T extends { component?: unknown; element?: unknown }> = Omit<T, 'component' | 'element'>;
+
+type AppointmentAddingOptions = Pick<AppointmentAddingEvent, 'appointmentData' | 'cancel'>;
+
+type AppointmentUpdatingOptions = Pick<AppointmentUpdatingEvent, 'newData' | 'oldData' | 'cancel'>;
+
+interface AppointmentCompletedOptions {
+  appointmentData: SafeAppointment;
+  error?: Error;
+}
+
+interface AppointmentDeletingOptions {
+  [key: string]: unknown;
+  appointmentData: SafeAppointment;
+  targetedAppointmentData?: SafeAppointment | AppointmentAdapter;
+  cancel: SchedulerActionCancel;
+}
+
+interface SchedulerActions {
+  onAppointmentAdding: (args: AppointmentAddingOptions) => void;
+  onAppointmentAdded: (args: AppointmentCompletedOptions) => void;
+  onAppointmentUpdating: (args: AppointmentUpdatingOptions) => void;
+  onAppointmentUpdated: (args: AppointmentCompletedOptions) => void;
+  onAppointmentDeleting: (args: AppointmentDeletingOptions) => void;
+  onAppointmentDeleted: (args: AppointmentCompletedOptions) => void;
+  onAppointmentFormOpening: (args: SchedulerEventArgs<AppointmentFormOpeningEvent>) => void;
+  onAppointmentTooltipShowing: (args: SchedulerEventArgs<AppointmentTooltipShowingEvent>) => void;
+  onSelectionEnd: (args: SchedulerEventArgs<SelectionEndEvent>) => void;
+  onAppointmentRendered: (args: AppointmentRenderedEvent) => void;
+  onAppointmentClick: (args: AppointmentClickEvent) => void;
+  onAppointmentDblClick: (args: AppointmentDblClickEvent) => void;
+  onAppointmentContextMenu: (args: AppointmentContextMenuEvent) => void;
+}
+
 class Scheduler extends SchedulerOptionsBaseWidget {
   // NOTE: Do not initialize variables here, because `_initMarkup` function runs before constructor,
   // and initialization in constructor will erase the data
@@ -211,9 +256,13 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
   resourceManager!: ResourceManager;
 
-  private actions: any;
+  private actions!: SchedulerActions;
 
-  _createActionByOption: any;
+  // TODO: used externally in workspaces/work_space.ts
+  declare _createActionByOption: (
+    optionName: string,
+    config?: { excludeValidators?: string[] },
+  ) => (event?: unknown) => void;
 
   private appointmentTooltip!: MobileTooltipStrategy | DesktopTooltipStrategy;
 
@@ -446,7 +495,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       case 'onAppointmentFormOpening':
       case 'onAppointmentTooltipShowing':
       case 'onSelectionEnd':
-        this.actions[name] = this._createActionByOption(name);
+        (this.actions as unknown as Record<string, (args: unknown) => void>)[name] = this._createActionByOption(name);
         break;
       case 'onAppointmentRendered':
         if (this.option('_newAppointments')) {
@@ -1063,14 +1112,14 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       onAppointmentClick: this._createActionByOption('onAppointmentClick'),
       onAppointmentDblClick: this._createActionByOption('onAppointmentDblClick'),
       onAppointmentContextMenu: this._createActionByOption('onAppointmentContextMenu'),
-    };
+    } as SchedulerActions;
   }
 
   // TODO<Appointments>: delete this method when old impl is removed
-  private getAppointmentRenderedAction() {
+  private getAppointmentRenderedAction(): (args: AppointmentRenderedEvent) => void {
     return this._createActionByOption('onAppointmentRendered', {
       excludeValidators: ['disabled', 'readOnly'],
-    });
+    }) as (args: AppointmentRenderedEvent) => void;
   }
 
   _renderFocusTarget(): void { return noop(); }
@@ -1130,7 +1179,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         appointmentCollectorTemplate: this.getViewOption('appointmentCollectorTemplate'),
 
         onAppointmentRendered: (...args) => this.actions.onAppointmentRendered(...args),
-        onAppointmentClick: (...args) => this.actions.onAppointmentClick(...args),
+        onAppointmentClick: (args: AppointmentClickEvent) => this.actions.onAppointmentClick(args),
         onAppointmentDblClick: (...args) => this.actions.onAppointmentDblClick(...args),
         onAppointmentContextMenu: (...args) => this.actions.onAppointmentContextMenu(...args),
         onDeleteKeyPress: (e) => {
@@ -1235,7 +1284,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       updateAppointment: (sourceAppointment, updatedAppointment) => this.updateAppointment(sourceAppointment, updatedAppointment),
 
     };
-    return new AppointmentPopup(scheduler, form);
+    return new AppointmentPopup(scheduler as never, form);
   }
 
   private scrollToAppointment(appointment: Record<string, unknown>): void {
@@ -1278,7 +1327,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       createEventArgs: that._createEventArgs.bind(that),
 
       newAppointments: Boolean(this.option('_newAppointments')),
-      onAppointmentClick: (...args) => this.actions.onAppointmentClick(...args),
+      onAppointmentClick: (args: AppointmentClickEvent) => this.actions.onAppointmentClick(args),
       onListInitialized: (e) => {
         if (this.option('_newAppointments')) {
           this.appointmentDragController.createTooltipDraggable(
@@ -1561,8 +1610,6 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       },
       onSelectionEnd: (args) => {
         this.actions.onSelectionEnd({
-          component: this,
-          element: this.$element(),
           selectedCellData: args.selectedCellData,
         });
       },
@@ -2097,7 +2144,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this._layoutManager;
   }
 
-  getActions() {
+  getActions(): SchedulerActions {
     return this.actions;
   }
 
@@ -2363,8 +2410,11 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.processDeleteAppointment(rawAppointment, deletingOptions);
   }
 
-  fireOnAppointmentDeleting(rawAppointment, targetedAppointmentData?: any) {
-    const deletingOptions = {
+  fireOnAppointmentDeleting(
+    rawAppointment: SafeAppointment,
+    targetedAppointmentData?: SafeAppointment | AppointmentAdapter,
+  ): AppointmentDeletingOptions {
+    const deletingOptions: AppointmentDeletingOptions = {
       appointmentData: rawAppointment,
       targetedAppointmentData,
       cancel: false,
@@ -2375,7 +2425,10 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return deletingOptions;
   }
 
-  processDeleteAppointment(rawAppointment, deletingOptions): void {
+  processDeleteAppointment(
+    rawAppointment: SafeAppointment,
+    deletingOptions: AppointmentDeletingOptions,
+  ): void {
     this.processActionResult(deletingOptions, function (canceled) {
       if (!canceled) {
         this.appointmentDataSource
@@ -2404,7 +2457,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       () => {
         this.processDeleteAppointment(
           appointment,
-          { cancel: false },
+          { appointmentData: appointment, cancel: false },
         );
       },
       true,

From 5dba430c307994af1e761f457429c44049fd9641 Mon Sep 17 00:00:00 2001
From: Sergei Burkatskii <noreply@github.com>
Date: Tue, 23 Jun 2026 12:08:04 +0200
Subject: [PATCH 07/17] refactor: type appointment collection options

---
 .../appointment_collection_options.ts         | 51 ++++++++++++++++
 .../js/__internal/scheduler/m_scheduler.ts    | 61 ++++++++++++-------
 .../tooltip_strategy_base.ts                  | 11 +++-
 .../js/__internal/scheduler/types.ts          | 12 ++++
 4 files changed, 110 insertions(+), 25 deletions(-)
 create mode 100644 packages/devextreme/js/__internal/scheduler/appointments/appointment_collection_options.ts

diff --git a/packages/devextreme/js/__internal/scheduler/appointments/appointment_collection_options.ts b/packages/devextreme/js/__internal/scheduler/appointments/appointment_collection_options.ts
new file mode 100644
index 000000000000..38e76729e96e
--- /dev/null
+++ b/packages/devextreme/js/__internal/scheduler/appointments/appointment_collection_options.ts
@@ -0,0 +1,51 @@
+import type {
+  AppointmentClickEvent,
+  AppointmentContextMenuEvent,
+  AppointmentDblClickEvent,
+  AppointmentRenderedEvent,
+} from '@js/ui/scheduler';
+
+import type NotifyScheduler from '../base/widget_notify_scheduler';
+import type { TimeZoneCalculator } from '../r1/timezone_calculator/index';
+import type { DesktopTooltipStrategy } from '../tooltip_strategies/desktop_tooltip_strategy';
+import type { MobileTooltipStrategy } from '../tooltip_strategies/mobile_tooltip_strategy';
+import type { DOMMetaData, ScrollToGroupValuesOrOptions } from '../types';
+import type { AppointmentDataAccessor } from '../utils/data_accessor/appointment_data_accessor';
+import type { ResourceManager } from '../utils/resource_manager/resource_manager';
+import type { AppointmentDataSource } from '../view_model/m_appointment_data_source';
+import type { SortedEntity } from '../view_model/types';
+import type ViewDataProvider from '../workspaces/view_model/view_data_provider';
+
+export interface AppointmentCollectionOptions {
+  getResourceManager: () => ResourceManager;
+  getAppointmentDataSource: () => AppointmentDataSource;
+  getSortedAppointments: () => SortedEntity[];
+  scrollTo: (
+    date: Date,
+    groupValuesOrOptions?: ScrollToGroupValuesOrOptions,
+    allDay?: boolean,
+  ) => void;
+  appointmentTooltip: MobileTooltipStrategy | DesktopTooltipStrategy;
+  dataAccessors: AppointmentDataAccessor;
+  notifyScheduler: NotifyScheduler;
+  onItemRendered: (args: AppointmentRenderedEvent) => void;
+  onItemClick: (args: AppointmentClickEvent) => void;
+  onItemContextMenu: (args: AppointmentContextMenuEvent) => void;
+  onAppointmentDblClick: (args: AppointmentDblClickEvent) => void;
+  tabIndex: number;
+  focusStateEnabled: boolean;
+  allowDrag: boolean;
+  allowDelete: boolean;
+  allowResize: boolean;
+  allowAllDayResize: boolean;
+  rtlEnabled: boolean;
+  groups: string[];
+  groupByDate: boolean;
+  timeZoneCalculator: TimeZoneCalculator;
+  getResizableStep: () => number;
+  getDOMElementsMetaData: () => DOMMetaData | undefined;
+  getViewDataProvider: () => ViewDataProvider | undefined;
+  isVerticalGroupedWorkSpace: () => boolean;
+  isDateAndTimeView: () => boolean;
+  onContentReady: () => void;
+}
diff --git a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
index b175b983bcd2..6a500350679e 100644
--- a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
+++ b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
@@ -31,6 +31,7 @@ import { hasWindow } from '@js/core/utils/window';
 import type { DataSourceOptions } from '@js/data/data_source';
 import DataHelperMixin from '@js/data_helper';
 import { custom as customDialog } from '@js/ui/dialog';
+import type { ItemContextMenuEvent } from '@js/ui/list';
 import type {
   Appointment,
   AppointmentAddingEvent,
@@ -56,6 +57,7 @@ import { AppointmentDragController } from './appointment_drag_controller';
 import type { AppointmentFormConfig } from './appointment_popup/form';
 import { AppointmentForm } from './appointment_popup/form';
 import { AppointmentPopup } from './appointment_popup/popup';
+import type { AppointmentCollectionOptions } from './appointments/appointment_collection_options';
 import AppointmentCollection from './appointments/m_appointment_collection';
 import type { AppointmentsProperties } from './appointments_new/appointments';
 import { Appointments } from './appointments_new/appointments';
@@ -80,9 +82,11 @@ import { validateRRule } from './recurrence/validate_rule';
 import { SchedulerOptionsBaseWidget } from './scheduler_options_base_widget';
 import { DesktopTooltipStrategy } from './tooltip_strategies/desktop_tooltip_strategy';
 import { MobileTooltipStrategy } from './tooltip_strategies/mobile_tooltip_strategy';
-import type { AppointmentTooltipExtraOptions } from './tooltip_strategies/tooltip_strategy_base';
+import type { AppointmentTooltipExtraOptions, AppointmentTooltipOptions } from './tooltip_strategies/tooltip_strategy_base';
 import type {
+  AppointmentTooltipContextMenuEventArgs,
   AppointmentTooltipItem,
+  MappedAppointmentFields,
   SafeAppointment,
   ScrollToGroupValuesOrOptions, ScrollToOptions, TargetedAppointment,
   ViewType,
@@ -1308,10 +1312,10 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this._workSpace.updateScrollPosition(startDate, appointmentGroupValues, inAllDayRow);
   }
 
-  private getAppointmentTooltipOptions() {
+  private getAppointmentTooltipOptions(): AppointmentTooltipOptions {
     const that = this;
     return {
-      // @ts-expect-error
+      // @ts-expect-error _createComponent is not defined in ts
       createComponent: that._createComponent.bind(that),
       container: that.$element(),
       getScrollableContainer: that.getWorkSpaceScrollableContainer.bind(that),
@@ -1321,7 +1325,12 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       checkAndDeleteAppointment: that.checkAndDeleteAppointment.bind(that),
       isAppointmentInAllDayPanel: that.isAppointmentInAllDayPanel.bind(that),
 
-      createFormattedDateText: (appointment, targetedAppointment, format) => this.fire('createFormattedDateText', appointment, targetedAppointment, format),
+      createFormattedDateText: (appointment, targetedAppointment, format) => this.fire(
+        'createFormattedDateText',
+        appointment,
+        (targetedAppointment ?? appointment) as TargetedAppointment,
+        format,
+      ),
       getAppointmentDisabled: (appointment) => this._dataAccessors.get('disabled', appointment),
       onItemContextMenu: that._createActionByOption('onAppointmentContextMenu'),
       createEventArgs: that._createEventArgs.bind(that),
@@ -1329,9 +1338,9 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       newAppointments: Boolean(this.option('_newAppointments')),
       onAppointmentClick: (args: AppointmentClickEvent) => this.actions.onAppointmentClick(args),
       onListInitialized: (e) => {
-        if (this.option('_newAppointments')) {
+        if (this.option('_newAppointments') && e.element) {
           this.appointmentDragController.createTooltipDraggable(
-            e.element,
+            $(e.element),
             {
               dragTemplate: this._appointments.renderDragClone.bind(this._appointments),
             },
@@ -1341,17 +1350,25 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       onListDisposing: () => {
         this.appointmentDragController.disposeTooltipDraggable();
       },
-    };
+    } satisfies AppointmentTooltipOptions;
   }
 
   // TODO<Appointments>: delete this method when old impl is removed
-  _createEventArgs(e) {
-    const config = {
-      itemData: e.itemData.appointment,
-      itemElement: e.itemElement,
-      targetedAppointment: e.itemData.targetedAppointment,
+  _createEventArgs(
+    e: ItemContextMenuEvent<AppointmentTooltipItem>,
+  ): AppointmentTooltipContextMenuEventArgs {
+    const config: {
+      itemData: SafeAppointment;
+      itemElement: dxElementWrapper;
+      targetedAppointment?: SafeAppointment | TargetedAppointment;
+    } = {
+      itemData: e.itemData!.appointment,
+      itemElement: $(e.itemElement),
+      targetedAppointment: e.itemData!.targetedAppointment,
     };
-    return extend({}, (this.fire as any)('mapAppointmentFields', config), {
+    const mappedFields = this.fire('mapAppointmentFields', config) as MappedAppointmentFields;
+
+    return extend({}, mappedFields, {
       component: e.component,
       element: e.element,
       event: e.event,
@@ -1464,8 +1481,8 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     };
   }
 
-  private appointmentsConfig() {
-    const config = {
+  private appointmentsConfig(): AppointmentCollectionOptions {
+    const config: AppointmentCollectionOptions = {
       getResourceManager: () => this.resourceManager,
       getAppointmentDataSource: () => this.appointmentDataSource,
       getSortedAppointments: () => this._layoutManager.sortedItems,
@@ -1474,18 +1491,18 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       dataAccessors: this._dataAccessors,
       notifyScheduler: this.notifyScheduler,
       onItemRendered: this.getAppointmentRenderedAction(),
-      onItemClick: this._createActionByOption('onAppointmentClick'),
-      onItemContextMenu: this._createActionByOption('onAppointmentContextMenu'),
-      onAppointmentDblClick: this._createActionByOption('onAppointmentDblClick'),
-      tabIndex: this.option('tabIndex'),
-      focusStateEnabled: this.option('focusStateEnabled'),
+      onItemClick: this._createActionByOption('onAppointmentClick') as (args: AppointmentClickEvent) => void,
+      onItemContextMenu: this._createActionByOption('onAppointmentContextMenu') as (args: AppointmentContextMenuEvent) => void,
+      onAppointmentDblClick: this._createActionByOption('onAppointmentDblClick') as (args: AppointmentDblClickEvent) => void,
+      tabIndex: this.option('tabIndex') ?? 0,
+      focusStateEnabled: Boolean(this.option('focusStateEnabled')),
       allowDrag: this.allowDragging(),
       allowDelete: this.editing.allowUpdating && this.editing.allowDeleting,
       allowResize: this.allowResizing(),
       allowAllDayResize: this.allowAllDayResizing(),
-      rtlEnabled: this.option('rtlEnabled'),
+      rtlEnabled: Boolean(this.option('rtlEnabled')),
       groups: this.getViewOption('groups'),
-      groupByDate: this.getViewOption('groupByDate'),
+      groupByDate: Boolean(this.getViewOption('groupByDate')),
       timeZoneCalculator: this.timeZoneCalculator,
       getResizableStep: () => (this._workSpace ? this._workSpace.positionHelper.getResizableStep() : 0),
       getDOMElementsMetaData: () => this._workSpace?.getDOMElementsMetaData(),
diff --git a/packages/devextreme/js/__internal/scheduler/tooltip_strategies/tooltip_strategy_base.ts b/packages/devextreme/js/__internal/scheduler/tooltip_strategies/tooltip_strategy_base.ts
index 0592e3c43d9c..f34d44d08455 100644
--- a/packages/devextreme/js/__internal/scheduler/tooltip_strategies/tooltip_strategy_base.ts
+++ b/packages/devextreme/js/__internal/scheduler/tooltip_strategies/tooltip_strategy_base.ts
@@ -19,7 +19,11 @@ import { createPromise } from '@ts/core/utils/promise';
 import List from '@ts/ui/list/list.edit';
 import type Tooltip from '@ts/ui/tooltip';
 
-import type { AppointmentTooltipItem, TargetedAppointment } from '../types';
+import type {
+  AppointmentTooltipContextMenuEventArgs,
+  AppointmentTooltipItem,
+  TargetedAppointment,
+} from '../types';
 
 const TOOLTIP_APPOINTMENT_ITEM = 'dx-tooltip-appointment-item';
 const TOOLTIP_APPOINTMENT_ITEM_CONTENT = `${TOOLTIP_APPOINTMENT_ITEM}-content`;
@@ -33,7 +37,7 @@ const TOOLTIP_APPOINTMENT_ITEM_DELETE_BUTTON = `${TOOLTIP_APPOINTMENT_ITEM}-dele
 
 const APPOINTMENT_TOOLTIP_TEMPLATE = 'appointmentTooltipTemplate';
 
-interface AppointmentTooltipOptions {
+export interface AppointmentTooltipOptions {
   createComponent: (
     element: dxElementWrapper,
     component: unknown,
@@ -63,7 +67,8 @@ interface AppointmentTooltipOptions {
   };
   getAppointmentDisabled: (appointment: Appointment) => boolean | undefined;
   onItemContextMenu: (eventArgs: unknown) => void;
-  createEventArgs: (e: ItemContextMenuEvent<AppointmentTooltipItem>) => unknown;
+  createEventArgs: (e: ItemContextMenuEvent<AppointmentTooltipItem>) =>
+  AppointmentTooltipContextMenuEventArgs;
   newAppointments?: boolean; // TODO<Appointments>
   onAppointmentClick: (e: AppointmentClickEvent) => void;
   onListInitialized: (e: InitializedEvent) => void;
diff --git a/packages/devextreme/js/__internal/scheduler/types.ts b/packages/devextreme/js/__internal/scheduler/types.ts
index 7ddba344ba65..11d0bcbf465b 100644
--- a/packages/devextreme/js/__internal/scheduler/types.ts
+++ b/packages/devextreme/js/__internal/scheduler/types.ts
@@ -1,4 +1,5 @@
 import type { dxElementWrapper } from '@js/core/renderer';
+import type { ItemContextMenuEvent } from '@js/ui/list';
 import type { Appointment, Properties } from '@js/ui/scheduler';
 import type { Component } from '@ts/core/widget/component';
 
@@ -298,6 +299,17 @@ export interface AppointmentTooltipItem {
   settings: AppointmentItemViewModel;
 }
 
+export interface MappedAppointmentFields {
+  appointmentData: SafeAppointment;
+  appointmentElement: dxElementWrapper;
+  targetedAppointmentData: SafeAppointment | TargetedAppointment;
+}
+
+export type AppointmentTooltipContextMenuEventArgs = MappedAppointmentFields & Pick<
+  ItemContextMenuEvent<AppointmentTooltipItem>,
+  'component' | 'element' | 'event' | 'model'
+>;
+
 export interface CompactAppointmentOptions {
   $container: dxElementWrapper;
   coordinates: { top: number; left: number };

From 744c1bba0466a51d44e9374ce8262d56af9467d0 Mon Sep 17 00:00:00 2001
From: Sergei Burkatskii <noreply@github.com>
Date: Tue, 23 Jun 2026 12:11:41 +0200
Subject: [PATCH 08/17] refactor: type workSpace config

---
 .../js/__internal/scheduler/m_scheduler.ts    | 80 +++++++++++--------
 1 file changed, 46 insertions(+), 34 deletions(-)

diff --git a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
index 6a500350679e..53ac5add63c2 100644
--- a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
+++ b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
@@ -9,6 +9,7 @@ import $ from '@js/core/renderer';
 import { BindableTemplate } from '@js/core/templates/bindable_template';
 import { EmptyTemplate } from '@js/core/templates/empty_template';
 import type { FunctionTemplate } from '@js/core/templates/function_template';
+import type { TemplateBase } from '@js/core/templates/template_base';
 import Callbacks from '@js/core/utils/callbacks';
 import { noop } from '@js/core/utils/common';
 import { compileGetter } from '@js/core/utils/data';
@@ -42,6 +43,8 @@ import type {
   AppointmentRenderedEvent,
   AppointmentTooltipShowingEvent,
   AppointmentUpdatingEvent,
+  CellClickEvent,
+  CellContextMenuEvent,
   DayOfWeek,
   Occurrence,
   SelectionEndEvent,
@@ -89,6 +92,7 @@ import type {
   MappedAppointmentFields,
   SafeAppointment,
   ScrollToGroupValuesOrOptions, ScrollToOptions, TargetedAppointment,
+  ViewCellData,
   ViewType,
 } from './types';
 import { utils } from './utils';
@@ -111,7 +115,7 @@ import SchedulerTimelineDay from './workspaces/timeline_day';
 import SchedulerTimelineMonth from './workspaces/timeline_month';
 import SchedulerTimelineWeek from './workspaces/timeline_week';
 import type SchedulerWorkSpace from './workspaces/work_space';
-import type { DroppableCellData } from './workspaces/work_space';
+import type { DroppableCellData, WorkspaceOptionsInternal } from './workspaces/work_space';
 import SchedulerWorkSpaceDay from './workspaces/work_space_day';
 import SchedulerWorkSpaceMonth from './workspaces/work_space_month';
 import SchedulerWorkSpaceWeek from './workspaces/work_space_week';
@@ -1583,7 +1587,8 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     });
   }
 
-  private workSpaceConfig(currentViewOptions: NormalizedView) {
+  private workSpaceConfig(currentViewOptions: NormalizedView): WorkspaceOptionsInternal {
+    const cellDuration = this.option('cellDuration');
     const scrolling = this.getViewOption('scrolling');
     const isVirtualScrolling = scrolling.mode === 'virtual';
     const horizontalVirtualScrollingAllowed = isVirtualScrolling
@@ -1595,7 +1600,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       || horizontalVirtualScrollingAllowed
       || isTimelineView(currentViewOptions.type);
 
-    const result = extend({
+    const workSpaceOptions = extend({
       newAppointments: Boolean(this.option('_newAppointments')),
       resources: this.option('resources'),
       getResourceManager: () => this.resourceManager,
@@ -1606,13 +1611,12 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       startDayHour: this.option('startDayHour'),
       endDayHour: this.option('endDayHour'),
       viewOffset: this.getViewOffsetMs(),
-      tabIndex: this.option('tabIndex'),
-      accessKey: this.option('accessKey'),
-      focusStateEnabled: this.option('focusStateEnabled'),
-      cellDuration: this.option('cellDuration'),
+      tabIndex: this.option('tabIndex') ?? 0,
+      accessKey: this.option('accessKey') ?? '',
+      focusStateEnabled: Boolean(this.option('focusStateEnabled')),
       showAllDayPanel: this.option('showAllDayPanel'),
       showCurrentTimeIndicator: this.option('showCurrentTimeIndicator'),
-      indicatorTime: this.option('indicatorTime'),
+      indicatorTime: this.option('indicatorTime') ?? new Date(),
       indicatorUpdateInterval: this.option('indicatorUpdateInterval'),
       shadeUntilCurrentTime: this.option('shadeUntilCurrentTime'),
       crossScrollingEnabled,
@@ -1622,15 +1626,15 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       dateCellTemplate: this.option('dateCellTemplate'),
       allowMultipleCellSelection: this.option('allowMultipleCellSelection'),
       selectedCellData: this.option('selectedCellData'),
-      onSelectionChanged: (args) => {
+      onSelectionChanged: (args: { selectedCellData: ViewCellData[] }) => {
         this.option('selectedCellData', args.selectedCellData);
       },
-      onSelectionEnd: (args) => {
+      onSelectionEnd: (args: { selectedCellData: ViewCellData[] }) => {
         this.actions.onSelectionEnd({
           selectedCellData: args.selectedCellData,
         });
       },
-      groupByDate: this.getViewOption('groupByDate'),
+      groupByDate: Boolean(this.getViewOption('groupByDate')),
       skippedDays: this.getViewOption('hiddenWeekDays') as number[],
       scrolling,
       draggingMode: this.option('_draggingMode'),
@@ -1639,42 +1643,50 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       schedulerWidth: this.option('width'),
       allDayPanelMode: this.option('allDayPanelMode'),
       onSelectedCellsClick: this.showAddAppointmentPopup.bind(this),
-      renderAppointments: () => { this.renderAppointments(); },
-      onShowAllDayPanel: (value) => this.option('showAllDayPanel', value),
-      getHeaderHeight: () => utils.DOM.getHeaderHeight(this.header),
-      onScrollEnd: () => this._appointments.updateResizableArea(),
+      renderAppointments: (): void => { this.renderAppointments(); },
+      onShowAllDayPanel: (value: boolean) => this.option('showAllDayPanel', value),
+      getHeaderHeight: (): number => utils.DOM.getHeaderHeight(this.header),
+      onScrollEnd: (): void => this._appointments.updateResizableArea(),
       onInitialized: (e) => {
         if (this.option('_newAppointments')) {
           this.appointmentDragController.createWorkSpaceDraggable(
-            e.element,
+            $(e.element),
             {
               getAppointmentData: this._appointments.getAppointmentData.bind(this._appointments),
             },
           );
         }
       },
-      onDisposing: () => {
+      onDisposing: (): void => {
         if (this.option('_newAppointments')) {
           this.appointmentDragController.disposeWorkSpaceDraggable();
         }
       },
-
-    }, currentViewOptions);
-
-    result.notifyScheduler = this.notifyScheduler;
-    result.groups = this.resourceManager.groupResources();
-    result.onCellClick = this._createActionByOption('onCellClick');
-    result.onCellContextMenu = this._createActionByOption('onCellContextMenu');
-    result.currentDate = this.getViewOption('currentDate');
-    result.skippedDays = this.getViewOption('hiddenWeekDays') as number[];
-    result.hoursInterval = result.cellDuration / 60;
-    result.allDayExpanded = false;
-    result.dataCellTemplate = result.dataCellTemplate ? this._getTemplate(result.dataCellTemplate) : null;
-    result.timeCellTemplate = result.timeCellTemplate ? this._getTemplate(result.timeCellTemplate) : null;
-    result.resourceCellTemplate = result.resourceCellTemplate ? this._getTemplate(result.resourceCellTemplate) : null;
-    result.dateCellTemplate = result.dateCellTemplate ? this._getTemplate(result.dateCellTemplate) : null;
-
-    return result;
+      rtlEnabled: Boolean(this.option('rtlEnabled')),
+      hoursInterval: cellDuration / 60,
+      allDayExpanded: false,
+      currentDate: this.getViewOption('currentDate'),
+    }, currentViewOptions) as WorkspaceOptionsInternal;
+
+    workSpaceOptions.notifyScheduler = this.notifyScheduler;
+    workSpaceOptions.groups = this.resourceManager.groupResources();
+    workSpaceOptions.onCellClick = this._createActionByOption('onCellClick') as (e: CellClickEvent) => void;
+    workSpaceOptions.onCellContextMenu = this._createActionByOption('onCellContextMenu') as (e: CellContextMenuEvent) => void;
+    workSpaceOptions.skippedDays = this.getViewOption('hiddenWeekDays') as number[];
+    workSpaceOptions.dataCellTemplate = workSpaceOptions.dataCellTemplate
+      ? this._getTemplate(workSpaceOptions.dataCellTemplate) as TemplateBase
+      : null;
+    workSpaceOptions.timeCellTemplate = workSpaceOptions.timeCellTemplate
+      ? this._getTemplate(workSpaceOptions.timeCellTemplate) as TemplateBase
+      : null;
+    workSpaceOptions.resourceCellTemplate = workSpaceOptions.resourceCellTemplate
+      ? this._getTemplate(workSpaceOptions.resourceCellTemplate) as TemplateBase
+      : null;
+    workSpaceOptions.dateCellTemplate = workSpaceOptions.dateCellTemplate
+      ? this._getTemplate(workSpaceOptions.dateCellTemplate) as TemplateBase
+      : null;
+
+    return workSpaceOptions;
   }
 
   private waitAsyncTemplate(callback): void {

From 232fa0b4a21cf0186bd6fbe4bafae37593dddfba Mon Sep 17 00:00:00 2001
From: Sergei Burkatskii <noreply@github.com>
Date: Tue, 23 Jun 2026 12:16:54 +0200
Subject: [PATCH 09/17] refactor: type arguments in methods

---
 .../js/__internal/scheduler/m_scheduler.ts    | 179 ++++++++++++------
 1 file changed, 118 insertions(+), 61 deletions(-)

diff --git a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
index 53ac5add63c2..4cadf21c260e 100644
--- a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
+++ b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
@@ -47,6 +47,7 @@ import type {
   CellContextMenuEvent,
   DayOfWeek,
   Occurrence,
+  RecurrenceEditMode,
   SelectionEndEvent,
 } from '@js/ui/scheduler';
 import errors from '@js/ui/widget/ui.errors';
@@ -106,6 +107,7 @@ import { VIEWS } from './utils/options/constants_view';
 import type { NormalizedView, SafeSchedulerOptions } from './utils/options/types';
 import { getAppointmentGroupValues, setAppointmentGroupValues } from './utils/resource_manager/appointment_groups_utils';
 import { ResourceManager } from './utils/resource_manager/resource_manager';
+import type { GroupValues } from './utils/resource_manager/types';
 import timeZoneUtils, { type TimezoneLabel } from './utils_time_zone';
 import AppointmentLayoutManager from './view_model/appointments_layout_manager';
 import { AppointmentDataSource } from './view_model/m_appointment_data_source';
@@ -180,7 +182,9 @@ const StoreEventNames = {
 
   UPDATING: 'onAppointmentUpdating',
   UPDATED: 'onAppointmentUpdated',
-};
+} as const;
+
+type StoreEventName = typeof StoreEventNames[keyof typeof StoreEventNames];
 
 const RECURRENCE_EDITING_MODE = {
   SERIES: 'editSeries',
@@ -236,6 +240,22 @@ interface SchedulerActions {
   onAppointmentContextMenu: (args: AppointmentContextMenuEvent) => void;
 }
 
+interface SelectedCellsClickCellData {
+  startDate?: Date;
+  endDate?: Date;
+  startDateUTC: number;
+  endDateUTC: number;
+  allDay?: boolean;
+}
+
+interface SchedulerEditing {
+  allowAdding: boolean;
+  allowUpdating: boolean;
+  allowDeleting: boolean;
+  allowResizing: boolean;
+  allowDragging: boolean;
+}
+
 class Scheduler extends SchedulerOptionsBaseWidget {
   // NOTE: Do not initialize variables here, because `_initMarkup` function runs before constructor,
   // and initialization in constructor will erase the data
@@ -322,7 +342,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this.timeZoneCalculatorInstance;
   }
 
-  private postponeDataSourceLoading(promise?: any): void {
+  private postponeDataSourceLoading(promise?: DeferredObj<unknown>): void {
     this.postponedOperations.add('_reloadDataSource', this.reloadDataSource.bind(this), promise);
   }
 
@@ -690,7 +710,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
   }
 
-  private bringEditingModeToAppointments(editing): void {
+  private bringEditingModeToAppointments(editing: SchedulerEditing): void {
     const editingConfig: any = {
       allowDelete: editing.allowUpdating && editing.allowDeleting,
     };
@@ -805,7 +825,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
   }
 
-  _dimensionChanged(value, isForce = false): void {
+  _dimensionChanged(value: unknown, isForce = false): void {
     const isFixedHeight = typeof this.option('height') === 'number';
     const isFixedWidth = typeof this.option('width') === 'number';
 
@@ -855,7 +875,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     (this.$element() as any).toggleClass(WIDGET_ADAPTIVE_CLASS, this.option('adaptivityEnabled'));
   }
 
-  _visibilityChanged(visible): void {
+  _visibilityChanged(visible: boolean): void {
     visible && this._dimensionChanged(null, true);
   }
 
@@ -962,9 +982,11 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   // TODO<Appointments>: delete this method when old impl is removed
   private initAppointmentTemplate(): void {
     const { expr } = this._dataAccessors;
-    const createGetter = (property) => compileGetter(`appointmentData.${property}`);
+    const createGetter = (property: string): ((data: unknown) => unknown) => (
+      compileGetter(`appointmentData.${property}`) as (data: unknown) => unknown
+    );
 
-    const getDate = (getter) => (data) => {
+    const getDate = (getter: (data: unknown) => unknown) => (data: unknown) => {
       const value = getter(data);
       if (value instanceof Date) {
         return value.valueOf();
@@ -1380,15 +1402,19 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     });
   }
 
-  checkAndDeleteAppointment(appointment, targetedAppointment): void {
+  checkAndDeleteAppointment(
+    appointment: SafeAppointment,
+    targetedAppointment?: SafeAppointment | TargetedAppointment,
+  ): void {
+    const targetedData = targetedAppointment ?? appointment;
     const targetedAdapter = new AppointmentAdapter(
-      targetedAppointment,
+      targetedData,
       this._dataAccessors,
     );
     const deletingOptions = this.fireOnAppointmentDeleting(appointment, targetedAdapter);
     this.checkRecurringAppointment(
       appointment,
-      targetedAppointment,
+      targetedData,
       targetedAdapter.startDate,
       () => {
         this.processDeleteAppointment(appointment, deletingOptions);
@@ -1406,7 +1432,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     };
   }
 
-  isAppointmentInAllDayPanel(appointmentData): boolean {
+  isAppointmentInAllDayPanel(appointmentData: SafeAppointment | Appointment): boolean {
     const workSpace = this._workSpace;
     const itTakesAllDay = this.appointmentTakesAllDay(appointmentData);
 
@@ -1689,7 +1715,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return workSpaceOptions;
   }
 
-  private waitAsyncTemplate(callback): void {
+  private waitAsyncTemplate(callback: () => void): void {
     if (this._options.silent('templatesRenderAsynchronously')) {
       const timer = setTimeout(() => {
         callback();
@@ -1798,14 +1824,14 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   checkRecurringAppointment(
-    rawAppointment,
-    singleAppointment,
-    exceptionDate,
-    callback,
-    isDeleted,
-    isPopupEditing?: any,
-    dragEvent?: any,
-    recurrenceEditMode?: any,
+    rawAppointment: SafeAppointment,
+    singleAppointment: SafeAppointment,
+    exceptionDate: Date,
+    callback: () => void,
+    isDeleted: boolean,
+    isPopupEditing?: boolean,
+    dragEvent?: SchedulerDragEvent | null,
+    recurrenceEditMode?: RecurrenceEditMode,
     onCancel?: () => void,
   ): void {
     const recurrenceRule = this._dataAccessors.get('recurrenceRule', rawAppointment);
@@ -1821,7 +1847,14 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         callback();
         break;
       case 'occurrence':
-        this.excludeAppointmentFromSeries(rawAppointment, singleAppointment, exceptionDate, isDeleted, isPopupEditing, dragEvent);
+        this.excludeAppointmentFromSeries(
+          rawAppointment,
+          singleAppointment,
+          exceptionDate,
+          isDeleted,
+          Boolean(isPopupEditing),
+          dragEvent,
+        );
         break;
       default:
         if (dragEvent) {
@@ -1837,7 +1870,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
               singleAppointment,
               exceptionDate,
               isDeleted,
-              isPopupEditing,
+              Boolean(isPopupEditing),
               dragEvent,
             );
           })
@@ -1851,7 +1884,14 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
   }
 
-  private excludeAppointmentFromSeries(rawAppointment, newRawAppointment, exceptionDate, isDeleted, isPopupEditing, dragEvent): void {
+  private excludeAppointmentFromSeries(
+    rawAppointment: SafeAppointment,
+    newRawAppointment: SafeAppointment,
+    exceptionDate: Date,
+    isDeleted: boolean,
+    isPopupEditing: boolean,
+    dragEvent?: SchedulerDragEvent | null,
+  ): void {
     const appointment = excludeFromRecurrence(
       rawAppointment,
       exceptionDate,
@@ -1890,18 +1930,22 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
   }
 
-  private createRecurrenceException(appointment, exceptionDate): string {
+  private createRecurrenceException(
+    appointment: SafeAppointment & { recurrenceException?: string },
+    exceptionDate: Date,
+  ): string {
     const result: any[] = [];
 
     if (appointment.recurrenceException) {
       result.push(appointment.recurrenceException);
     }
-    result.push(this.getSerializedDate(exceptionDate, appointment.startDate, appointment.allDay));
+    const adapter = new AppointmentAdapter(appointment, this._dataAccessors);
+    result.push(this.getSerializedDate(exceptionDate, adapter.startDate, Boolean(adapter.allDay)));
 
     return result.join();
   }
 
-  private getSerializedDate(date, startDate, isAllDay): string {
+  private getSerializedDate(date: Date, startDate: Date, isAllDay: boolean): string {
     isAllDay && date.setHours(
       startDate.getHours(),
       startDate.getMinutes(),
@@ -1941,7 +1985,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   getUpdatedData(rawAppointment: Appointment, $cell?: dxElementWrapper): SafeAppointment {
     const viewOffset = this.getViewOffsetMs();
 
-    const getConvertedFromGrid = (date: any): Date | undefined => {
+    const getConvertedFromGrid = (date: Date | undefined): Date | undefined => {
       if (!date) {
         return undefined;
       }
@@ -2037,7 +2081,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     );
   }
 
-  subscribe(subject, action): void {
+  subscribe<K extends SubscribeKey>(subject: K, action: SubscribeMethods[K]): void {
     this.subscribes[subject] = subscribes[subject] = action;
   }
 
@@ -2062,7 +2106,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     target: SafeAppointment,
     rawAppointment: SafeAppointment,
     onUpdatePrevented?: () => void,
-    dragEvent?: SchedulerDragEvent,
+    dragEvent?: SchedulerDragEvent | null,
   ): Promise<void> {
     const updatingOptions = {
       newData: rawAppointment,
@@ -2070,7 +2114,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       cancel: false,
     };
 
-    const performFailAction = function (err?: any) {
+    const performFailAction = function (this: Scheduler, err?: Error): void {
       if (onUpdatePrevented) {
         onUpdatePrevented.call(this);
       }
@@ -2107,8 +2151,8 @@ class Scheduler extends SchedulerOptionsBaseWidget {
               this.onDataPromiseCompleted(StoreEventNames.UPDATED, storeAppointment);
             })
             .fail(() => performFailAction());
-        } catch (err) {
-          performFailAction(err);
+        } catch (err: unknown) {
+          performFailAction(err instanceof Error ? err : undefined);
           this.updatingAppointments.delete(target);
           deferred.resolve();
         }
@@ -2146,13 +2190,17 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return deferred.promise();
   }
 
-  private expandAllDayPanel(appointment): void {
+  private expandAllDayPanel(appointment: SafeAppointment | Appointment): void {
     if (!this.isAllDayExpanded() && this.appointmentTakesAllDay(appointment)) {
       this.updateOption('workSpace', 'allDayExpanded', true);
     }
   }
 
-  private onDataPromiseCompleted(handlerName, storeAppointment, appointment?: any): void {
+  private onDataPromiseCompleted(
+    handlerName: StoreEventName,
+    storeAppointment: SafeAppointment | Error,
+    appointment?: SafeAppointment,
+  ): void {
     const args: any = { appointmentData: appointment || storeAppointment };
 
     if (storeAppointment instanceof Error) {
@@ -2177,7 +2225,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this.actions;
   }
 
-  appointmentTakesAllDay(rawAppointment): boolean {
+  appointmentTakesAllDay(rawAppointment: SafeAppointment | Appointment): boolean {
     const appointment = new AppointmentAdapter(
       rawAppointment,
       this._dataAccessors,
@@ -2189,8 +2237,8 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     );
   }
 
-  dayHasAppointment(day, rawAppointment, trimTime): boolean {
-    const getConvertedToTimeZone = (date) => this.timeZoneCalculator.createDate(date, 'toGrid');
+  dayHasAppointment(day: Date, rawAppointment: SafeAppointment | Appointment, trimTime: boolean): boolean {
+    const getConvertedToTimeZone = (date: Date): Date => this.timeZoneCalculator.createDate(date, 'toGrid');
 
     const appointment = new AppointmentAdapter(
       rawAppointment,
@@ -2228,36 +2276,40 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this._workSpace.getEndViewDate();
   }
 
-  showAddAppointmentPopup(cellData, cellGroups): void {
+  showAddAppointmentPopup(cellData: SelectedCellsClickCellData, cellGroups: GroupValues): void {
     const appointmentAdapter = new AppointmentAdapter({}, this._dataAccessors);
 
     appointmentAdapter.allDay = Boolean(cellData.allDay);
-    appointmentAdapter.startDate = cellData.startDateUTC;
-    appointmentAdapter.endDate = cellData.endDateUTC;
+    appointmentAdapter.startDate = new Date(cellData.startDateUTC);
+    appointmentAdapter.endDate = new Date(cellData.endDateUTC);
 
     const resultAppointment = extend(appointmentAdapter.source, cellGroups);
     this.showAppointmentPopup(resultAppointment, true);
   }
 
-  showAppointmentPopup(rawAppointment?: any, createNewAppointment?: boolean, rawTargetedAppointment?: any): void {
-    const newRawTargetedAppointment = { ...rawTargetedAppointment };
-    if (newRawTargetedAppointment) {
+  showAppointmentPopup(
+    rawAppointment?: SafeAppointment,
+    createNewAppointment?: boolean,
+    rawTargetedAppointment?: SafeAppointment | TargetedAppointment,
+  ): void {
+    const newRawTargetedAppointment = rawTargetedAppointment
+      ? { ...rawTargetedAppointment }
+      : {} as SafeAppointment;
+    if (rawTargetedAppointment) {
       delete newRawTargetedAppointment.displayStartDate;
       delete newRawTargetedAppointment.displayEndDate;
     }
 
-    const newTargetedAppointment = extend({}, rawAppointment, newRawTargetedAppointment);
-
     const isCreateAppointment = createNewAppointment ?? isEmptyObject(rawAppointment);
 
-    if (isEmptyObject(rawAppointment)) {
-      rawAppointment = this.createPopupAppointment();
-    }
-
     if (isCreateAppointment) {
+      const appointmentData = isEmptyObject(rawAppointment)
+        ? this.createPopupAppointment()
+        : rawAppointment as SafeAppointment;
+
       delete this.editAppointmentData; // TODO
       if (this.editing.allowAdding) {
-        this.appointmentPopup.show(rawAppointment, {
+        this.appointmentPopup.show(appointmentData, {
           onSave: (appointment) => when(this.addAppointment(appointment))
             .done(() => this.scrollToAppointment(appointment)),
           title: messageLocalization.format('dxScheduler-newPopupTitle'),
@@ -2265,17 +2317,22 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         });
       }
     } else {
-      const startDate = this._dataAccessors.get('startDate', newRawTargetedAppointment || rawAppointment);
+      const appointmentData = rawAppointment as SafeAppointment;
+      const newTargetedAppointment = extend({}, appointmentData, newRawTargetedAppointment) as SafeAppointment;
+      const startDate = this._dataAccessors.get(
+        'startDate',
+        Object.keys(newRawTargetedAppointment).length ? newRawTargetedAppointment : appointmentData,
+      );
 
-      this.checkRecurringAppointment(rawAppointment, newTargetedAppointment, startDate, () => {
-        this.editAppointmentData = rawAppointment; // TODO
+      this.checkRecurringAppointment(appointmentData, newTargetedAppointment, startDate, () => {
+        this.editAppointmentData = appointmentData; // TODO
 
-        const adapter = new AppointmentAdapter(rawAppointment, this._dataAccessors);
+        const adapter = new AppointmentAdapter(appointmentData, this._dataAccessors);
         const isDisabled = Boolean(adapter.source) && adapter.disabled;
         const readOnly = isDisabled || !this.editing.allowUpdating;
 
-        this.appointmentPopup.show(rawAppointment, {
-          onSave: (appointment) => when(this.updateAppointment(rawAppointment, appointment))
+        this.appointmentPopup.show(appointmentData, {
+          onSave: (appointment) => when(this.updateAppointment(appointmentData, appointment))
             .done(() => this.scrollToAppointment(appointment)),
           title: messageLocalization.format('dxScheduler-editPopupTitle'),
           readOnly,
@@ -2297,7 +2354,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return result;
   }
 
-  hideAppointmentPopup(saveChanges?: any): void {
+  hideAppointmentPopup(saveChanges?: boolean): void {
     if (this.appointmentPopup?.visible) {
       saveChanges && this.appointmentPopup.saveChangesAsync();
       this.appointmentPopup.hide();
@@ -2434,7 +2491,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this.updateAppointmentCore(target, appointment);
   }
 
-  deleteAppointment(rawAppointment): void {
+  deleteAppointment(rawAppointment: SafeAppointment): void {
     const deletingOptions = this.fireOnAppointmentDeleting(rawAppointment);
     this.processDeleteAppointment(rawAppointment, deletingOptions);
   }
@@ -2472,9 +2529,9 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   deleteRecurrence(
-    appointment,
+    appointment: SafeAppointment,
     date: Date | string,
-    recurrenceEditMode,
+    recurrenceEditMode: RecurrenceEditMode,
   ): void {
     if (typeof date === 'string') {
       date = new Date(date);
@@ -2491,7 +2548,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       },
       true,
       false,
-      null,
+      undefined,
       recurrenceEditMode,
     );
   }

From f8695c1b93f8c576bfec7cc2823cafcea3e94c17 Mon Sep 17 00:00:00 2001
From: Sergei Burkatskii <noreply@github.com>
Date: Tue, 23 Jun 2026 13:15:29 +0200
Subject: [PATCH 10/17] refactor: enhance type definitions and improve type
 safety in scheduler

---
 .../js/__internal/scheduler/m_scheduler.ts    | 569 +++++++++++-------
 1 file changed, 362 insertions(+), 207 deletions(-)

diff --git a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
index 4cadf21c260e..ec6f956a02d6 100644
--- a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
+++ b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
@@ -1,9 +1,12 @@
+/* eslint-disable devextreme-custom/no-deferred */
 import { triggerResizeEvent } from '@js/common/core/events/visibility_change';
 import dateLocalization from '@js/common/core/localization/date';
 import messageLocalization from '@js/common/core/localization/message';
+import type { DataSource } from '@js/common/data';
 import registerComponent from '@js/core/component_registrator';
 import config from '@js/core/config';
 import { getPublicElement } from '@js/core/element';
+import type { PostponedOperations } from '@js/core/postponed_operations';
 import type { dxElementWrapper } from '@js/core/renderer';
 import $ from '@js/core/renderer';
 import { BindableTemplate } from '@js/core/templates/bindable_template';
@@ -31,6 +34,7 @@ import {
 import { hasWindow } from '@js/core/utils/window';
 import type { DataSourceOptions } from '@js/data/data_source';
 import DataHelperMixin from '@js/data_helper';
+import type { CustomDialogOptions } from '@js/ui/dialog';
 import { custom as customDialog } from '@js/ui/dialog';
 import type { ItemContextMenuEvent } from '@js/ui/list';
 import type {
@@ -47,10 +51,12 @@ import type {
   CellContextMenuEvent,
   DayOfWeek,
   Occurrence,
+  Properties as SchedulerProperties,
   RecurrenceEditMode,
   SelectionEndEvent,
 } from '@js/ui/scheduler';
 import errors from '@js/ui/widget/ui.errors';
+import type { Options } from '@ts/core/options/m_index';
 import { dateUtilsTs } from '@ts/core/utils/date';
 import type { OptionChanged } from '@ts/core/widget/types';
 import type Scrollable from '@ts/ui/scroll_view/scrollable';
@@ -90,6 +96,7 @@ import type { AppointmentTooltipExtraOptions, AppointmentTooltipOptions } from '
 import type {
   AppointmentTooltipContextMenuEventArgs,
   AppointmentTooltipItem,
+  CreateComponentFn,
   MappedAppointmentFields,
   SafeAppointment,
   ScrollToGroupValuesOrOptions, ScrollToOptions, TargetedAppointment,
@@ -111,7 +118,7 @@ import type { GroupValues } from './utils/resource_manager/types';
 import timeZoneUtils, { type TimezoneLabel } from './utils_time_zone';
 import AppointmentLayoutManager from './view_model/appointments_layout_manager';
 import { AppointmentDataSource } from './view_model/m_appointment_data_source';
-import type { AppointmentViewModelPlain } from './view_model/types';
+import type { AppointmentViewModelPlain, AppointmentItemViewModel } from './view_model/types';
 import SchedulerAgenda from './workspaces/agenda';
 import SchedulerTimelineDay from './workspaces/timeline_day';
 import SchedulerTimelineMonth from './workspaces/timeline_month';
@@ -256,30 +263,69 @@ interface SchedulerEditing {
   allowDragging: boolean;
 }
 
+type SchedulerEditingObject = Exclude<NonNullable<SchedulerProperties['editing']>, boolean>;
+
+type SchedulerEditingState = SchedulerEditing & Partial<SchedulerEditingObject>;
+
+interface RecurrenceDialog {
+  show: () => DeferredObj<string>;
+  hide: (mode: string) => void;
+}
+
+type AppointmentsEditingOptions = Partial<{
+  allowDelete: boolean;
+  allowDrag: boolean;
+  allowResize: boolean;
+  allowAllDayResize: boolean;
+}>;
+
+interface SchedulerAppointmentsHost {
+  option(options: Record<string, unknown>): unknown;
+  option(name: string, value?: unknown): unknown;
+  repaint(): void;
+  $element(): dxElementWrapper;
+  focus(): void;
+  moveAppointmentBack(dragEvent?: SchedulerDragEvent | null): void;
+  updateResizableArea(): void;
+  renderDragClone(...args: unknown[]): dxElementWrapper;
+  getAppointmentData(...args: unknown[]): unknown;
+}
+
 class Scheduler extends SchedulerOptionsBaseWidget {
   // NOTE: Do not initialize variables here, because `_initMarkup` function runs before constructor,
   // and initialization in constructor will erase the data
   private timeZoneCalculatorInstance: TimeZoneCalculator | null = null;
 
-  postponedOperations: any;
+  declare postponedOperations: PostponedOperations;
+
+  declare _disposed?: boolean;
+
+  declare _options: Options;
 
   private a11yStatus!: dxElementWrapper;
 
-  // TODO: used externally in m_appointment_drag_behavior.ts, m_subscribes.ts, workspaces/work_space.ts
+  // TODO: used externally in m_appointment_drag_behavior.ts,
+  // m_subscribes.ts, workspaces/work_space.ts
   _workSpace!: SchedulerWorkSpace;
 
   private header?: SchedulerHeader;
 
-  // TODO: used externally in m_appointment_drag_behavior.ts, m_subscribes.ts, workspaces/work_space.ts
-  _appointments: any;
+  // TODO: used externally in m_appointment_drag_behavior.ts,
+  // m_subscribes.ts, workspaces/work_space.ts
+  _appointments!: SchedulerAppointmentsHost;
 
   private appointmentDragController!: AppointmentDragController;
 
   appointmentDataSource!: AppointmentDataSource;
 
-  _dataSource: any;
+  declare _dataSource: DataSource | undefined;
 
-  // TODO: used externally in m_subscribes.ts, view_model/preparation/prepare_appointments.ts, view_model/filtration/utils/get_filter_options/get_filter_options.ts
+  // TODO: used externally in workspaces/work_space.ts
+  declare _createComponent: CreateComponentFn;
+
+  // TODO: used externally in m_subscribes.ts,
+  // view_model/preparation/prepare_appointments.ts,
+  // view_model/filtration/utils/get_filter_options/get_filter_options.ts
   _dataAccessors!: AppointmentDataAccessor;
 
   resourceManager!: ResourceManager;
@@ -296,41 +342,37 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
   private readyToRenderAppointments?: boolean;
 
-  private editing: any;
+  private editing!: SchedulerEditingState;
 
-  private workSpaceRecalculation: any;
+  private workSpaceRecalculation!: DeferredObj<void>;
 
-  private appointmentPopup: any;
+  private appointmentPopup!: AppointmentPopup;
 
   // TODO: used externally in m_subscribes.ts
   _compactAppointmentsHelper!: CompactAppointmentsHelper;
 
-  private asyncTemplatesTimers!: any[];
+  private asyncTemplatesTimers: ReturnType<typeof setTimeout>[] = [];
 
   private readonly updatingAppointments: Set<Appointment> = new Set();
 
-  private dataSourceLoadedCallback: any;
+  private dataSourceLoadedCallback!: ReturnType<typeof Callbacks>;
 
-  private subscribes: any;
+  private subscribes: SubscribeMethods = subscribes;
 
   private notifyScheduler!: NotifyScheduler;
 
-  private recurrenceDialog: any;
+  private recurrenceDialog?: RecurrenceDialog;
 
   // TODO: used externally in m_subscribes.ts
   _layoutManager!: AppointmentLayoutManager;
 
-  private appointmentForm: any;
+  private appointmentForm!: AppointmentForm;
 
-  private mainContainer: any;
+  private mainContainer!: dxElementWrapper;
 
   private $draggableContainer?: dxElementWrapper;
 
-  private readonly all: any;
-
-  _options: any;
-
-  private editAppointmentData: any;
+  private editAppointmentData?: SafeAppointment;
 
   private timeZonesPromise!: Promise<TimezoneLabel[]>;
 
@@ -350,8 +392,8 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     const whenLoaded = this.postponedOperations.add('loadResources', () => {
       const groups = this.getViewOption('groups');
 
-      return fromPromise(this.resourceManager.loadGroupResources(groups, forceReload));
-    });
+      return when(this.resourceManager.loadGroupResources(groups, forceReload));
+    }, undefined);
 
     const resolveCallbacks: DeferredObj<void> = Deferred();
 
@@ -395,16 +437,18 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         this._initDataSource();
 
         this.postponeResourceLoading().done(() => {
-          this.appointmentDataSource.setDataSource(this._dataSource);
+          if (this._dataSource) {
+            this.appointmentDataSource.setDataSource(this._dataSource);
+          }
           this.setRemoteFilterIfNeeded();
           this.updateOption('workSpace', 'showAllDayPanel', this.option('showAllDayPanel'));
         });
         break;
       case 'min':
       case 'max': {
-        const value = this.getViewOption(name);
-        this.updateOption('header', name, value);
-        this.updateOption('workSpace', name, value);
+        const viewValue = this.getViewOption(name);
+        this.updateOption('header', name, viewValue);
+        this.updateOption('workSpace', name, viewValue);
         break;
       }
       case 'views':
@@ -523,7 +567,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       case 'onAppointmentFormOpening':
       case 'onAppointmentTooltipShowing':
       case 'onSelectionEnd':
-        (this.actions as unknown as Record<string, (args: unknown) => void>)[name] = this._createActionByOption(name);
+        this.actions[name] = this._createActionByOption(name);
         break;
       case 'onAppointmentRendered':
         if (this.option('_newAppointments')) {
@@ -700,9 +744,11 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         this.updateOption('workSpace', 'draggingMode', value);
         break;
       case 'toolbar':
-        this.header
-          ? this.header.onToolbarOptionChanged(args.fullName, value)
-          : this.repaint();
+        if (this.header) {
+          this.header.onToolbarOptionChanged(args.fullName, value);
+        } else {
+          this.repaint();
+        }
         break;
       default:
         // @ts-expect-error
@@ -711,7 +757,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   private bringEditingModeToAppointments(editing: SchedulerEditing): void {
-    const editingConfig: any = {
+    const editingConfig: AppointmentsEditingOptions = {
       allowDelete: editing.allowUpdating && editing.allowDeleting,
     };
 
@@ -784,11 +830,11 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     const result: DeferredObj<void> = Deferred();
 
     if (this._dataSource) {
-      this._dataSource.load().done(() => {
+      void this._dataSource.load().then(() => {
         hideLoading().catch(noop);
 
         this._fireContentReadyAction(result);
-      }).fail(() => {
+      }).catch(() => {
         hideLoading().catch(noop);
         result.reject();
       });
@@ -797,7 +843,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         showLoading({
           container: this.$element().get(0),
           position: {
-            of: this.$element() as any,
+            of: this.$element().get(0),
           },
         }).catch(noop);
       }
@@ -811,13 +857,13 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   _fireContentReadyAction(result?: DeferredObj<void>): void {
     // @ts-expect-error
     const contentReadyBase = super._fireContentReadyAction.bind(this);
-    const fireContentReady = () => {
+    const fireContentReady = (): void => {
       contentReadyBase();
       result?.resolve();
     };
 
-    if (this.workSpaceRecalculation) {
-      this.workSpaceRecalculation?.done(() => {
+    if (this.workSpaceRecalculation?.state() === 'pending') {
+      this.workSpaceRecalculation.done(() => {
         fireContentReady();
       });
     } else {
@@ -867,16 +913,19 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   private toggleSmallClass(): void {
-    const { width } = getBoundingRect((this.$element() as any).get(0));
-    (this.$element() as any).toggleClass(WIDGET_SMALL_CLASS, width < WIDGET_SMALL_WIDTH);
+    const element = this.$element().get(0);
+    const { width } = getBoundingRect(element);
+    this.$element().toggleClass(WIDGET_SMALL_CLASS, width < WIDGET_SMALL_WIDTH);
   }
 
   private toggleAdaptiveClass(): void {
-    (this.$element() as any).toggleClass(WIDGET_ADAPTIVE_CLASS, this.option('adaptivityEnabled'));
+    (this.$element()).toggleClass(WIDGET_ADAPTIVE_CLASS, this.option('adaptivityEnabled'));
   }
 
   _visibilityChanged(visible: boolean): void {
-    visible && this._dimensionChanged(null, true);
+    if (visible) {
+      this._dimensionChanged(null, true);
+    }
   }
 
   _dataSourceOptions(): DataSourceOptions {
@@ -914,7 +963,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
     this.customizeDataSourceLoadOptions();
 
-    (this.$element() as any).addClass(WIDGET_CLASS);
+    this.$element().addClass(WIDGET_CLASS);
 
     this.initEditing();
 
@@ -936,9 +985,11 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
     this.appointmentDragController = new AppointmentDragController({
       component: this,
-      $draggableContainer: () => this.$draggableContainer!,
+      $draggableContainer: (): dxElementWrapper => this.$draggableContainer ?? this.$element(),
       canDragAppointment: this.canDragAppointment.bind(this),
-      getCellFromDragTarget: ($dragTarget) => this._workSpace.getCellFromDragTarget($dragTarget),
+      getCellFromDragTarget: ($dragTarget: dxElementWrapper): dxElementWrapper | null => (
+        this._workSpace.getCellFromDragTarget($dragTarget)
+      ),
 
       // @ts-expect-error _createComponent is not defined in ts
       createComponent: this._createComponent.bind(this),
@@ -950,6 +1001,9 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
   createAppointmentDataSource(): void {
     this.appointmentDataSource?.destroy();
+    if (!this._dataSource) {
+      return;
+    }
     this.appointmentDataSource = new AppointmentDataSource(this._dataSource);
   }
 
@@ -962,6 +1016,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   private customizeDataSourceLoadOptions(): void {
+    // @ts-expect-error customizeStoreLoadOptions is a custom DataSource event
     this._dataSource?.on('customizeStoreLoadOptions', ({ storeLoadOptions }) => {
       storeLoadOptions.startDate = this.getStartViewDate();
       storeLoadOptions.endDate = this.getEndViewDate();
@@ -986,7 +1041,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       compileGetter(`appointmentData.${property}`) as (data: unknown) => unknown
     );
 
-    const getDate = (getter: (data: unknown) => unknown) => (data: unknown) => {
+    const getDate = (getter: (data: unknown) => unknown) => (data: unknown): unknown => {
       const value = getter(data);
       if (value instanceof Date) {
         return value.valueOf();
@@ -996,7 +1051,8 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
     this._templateManager.addDefaultTemplates({
       item: new BindableTemplate(
-        ($container, data, model) => this.getAppointmentsInstance()._renderAppointmentTemplate($container, data, model),
+        ($container, data, model) => this.getAppointmentsInstance()
+          ._renderAppointmentTemplate($container, data, model),
         [
           'html',
           'text',
@@ -1106,7 +1162,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       popup: undefined,
     }).every((value) => !value);
 
-    (this.$element() as any).toggleClass(WIDGET_READONLY_CLASS, isReadOnly);
+    this.$element().toggleClass(WIDGET_READONLY_CLASS, isReadOnly);
   }
 
   _dispose(): void {
@@ -1180,9 +1236,9 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   private initMarkupOnResourceLoaded(): void {
-    if (!(this as any)._disposed) {
+    if (!this._disposed) {
       this.initMarkupCore();
-      this.reloadDataSource();
+      this.reloadDataSource().catch(noop);
     }
   }
 
@@ -1219,7 +1275,13 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         getResourceManager: () => this.resourceManager,
         getAppointmentDataSource: () => this.appointmentDataSource,
         getDataAccessor: () => this._dataAccessors,
-        getStartViewDate: (): Date => this.getStartViewDate()!,
+        getStartViewDate: (): Date => {
+          const startViewDate = this.getStartViewDate();
+          if (!startViewDate) {
+            throw errors.Error('E0001');
+          }
+          return startViewDate;
+        },
         getSortedItems: () => this._layoutManager.sortedItems,
 
         isVirtualScrolling: () => this.isVirtualScrolling(),
@@ -1246,14 +1308,15 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     // @ts-expect-error
     if (this.isDataSourceLoaded() || this._isDataSourceLoading()) {
       this.initMarkupCore();
-      this._dataSourceChangedHandler(this._dataSource.items());
+      this._dataSourceChangedHandler(this._dataSource?.items() ?? []);
       this._fireContentReadyAction();
     } else {
       const groups = this.getViewOption('groups');
 
       if (groups?.length) {
         this.resourceManager.loadGroupResources(groups, true)
-          .then(() => this.initMarkupOnResourceLoaded());
+          .then(() => this.initMarkupOnResourceLoaded())
+          .catch(noop);
       } else {
         this.initMarkupOnResourceLoaded();
       }
@@ -1280,38 +1343,50 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   createAppointmentForm(): AppointmentForm {
-    const config: AppointmentFormConfig = {
+    const appointmentFormConfig: AppointmentFormConfig = {
       dataAccessors: this._dataAccessors,
       editing: this.editing,
       resourceManager: this.resourceManager,
       firstDayOfWeek: this.getFirstDayOfWeek(),
       startDayHour: this.option('startDayHour') ?? 0,
       // @ts-expect-error
-      createComponent: (element, component, options) => this._createComponent(element, component, options),
-      getCalculatedEndDate: (startDateWithStartHour) => this._workSpace.calculateEndDate(startDateWithStartHour),
+      createComponent: this._createComponent.bind(this),
+      getCalculatedEndDate: (startDateWithStartHour: Date): Date => (
+        this._workSpace.calculateEndDate(startDateWithStartHour)
+      ),
     };
 
-    return new AppointmentForm(config);
+    return new AppointmentForm(appointmentFormConfig);
   }
 
   createAppointmentPopup(form: AppointmentForm): AppointmentPopup {
     const scheduler = {
-      getElement: () => this.$element(),
+      getElement: (): dxElementWrapper => this.$element(),
       // @ts-expect-error
-      createComponent: (element, component, options) => this._createComponent(element, component, options),
-      focus: () => this.focus(),
+      createComponent: this._createComponent.bind(this),
+      focus: (): void => { this.focus(); },
 
-      getResourceManager: () => this.resourceManager,
+      getResourceManager: (): ResourceManager => this.resourceManager,
 
-      getEditingConfig: () => this.editing,
+      getEditingConfig: (): SchedulerEditingState => this.editing,
 
       getTimeZoneCalculator: (): TimeZoneCalculator => this.timeZoneCalculator,
-      getDataAccessors: () => this._dataAccessors,
-      getAppointmentFormOpening: () => this.actions.onAppointmentFormOpening,
-      processActionResult: (arg, canceled) => this.processActionResult(arg, canceled),
+      getDataAccessors: (): AppointmentDataAccessor => this._dataAccessors,
+      getAppointmentFormOpening: (): SchedulerActions['onAppointmentFormOpening'] => (
+        this.actions.onAppointmentFormOpening
+      ),
+      processActionResult: (
+        arg: SchedulerActionOptions,
+        canceled: ProcessActionCallback,
+      ): Promise<void> => this.processActionResult(arg, canceled),
 
-      addAppointment: (appointment) => this.addAppointment(appointment),
-      updateAppointment: (sourceAppointment, updatedAppointment) => this.updateAppointment(sourceAppointment, updatedAppointment),
+      addAppointment: (appointment: SafeAppointment): Promise<void> => (
+        this.addAppointment(appointment)
+      ),
+      updateAppointment: (
+        sourceAppointment: SafeAppointment,
+        updatedAppointment: SafeAppointment,
+      ): Promise<void> => this.updateAppointment(sourceAppointment, updatedAppointment),
 
     };
     return new AppointmentPopup(scheduler as never, form);
@@ -1339,17 +1414,16 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   private getAppointmentTooltipOptions(): AppointmentTooltipOptions {
-    const that = this;
     return {
       // @ts-expect-error _createComponent is not defined in ts
-      createComponent: that._createComponent.bind(that),
-      container: that.$element(),
-      getScrollableContainer: that.getWorkSpaceScrollableContainer.bind(that),
-      addDefaultTemplates: that._templateManager.addDefaultTemplates.bind(that._templateManager),
-      getAppointmentTemplate: that.getAppointmentTemplate.bind(that),
-      showAppointmentPopup: that.showAppointmentPopup.bind(that),
-      checkAndDeleteAppointment: that.checkAndDeleteAppointment.bind(that),
-      isAppointmentInAllDayPanel: that.isAppointmentInAllDayPanel.bind(that),
+      createComponent: this._createComponent.bind(this),
+      container: this.$element(),
+      getScrollableContainer: this.getWorkSpaceScrollableContainer.bind(this),
+      addDefaultTemplates: this._templateManager.addDefaultTemplates.bind(this._templateManager),
+      getAppointmentTemplate: this.getAppointmentTemplate.bind(this),
+      showAppointmentPopup: this.showAppointmentPopup.bind(this),
+      checkAndDeleteAppointment: this.checkAndDeleteAppointment.bind(this),
+      isAppointmentInAllDayPanel: this.isAppointmentInAllDayPanel.bind(this),
 
       createFormattedDateText: (appointment, targetedAppointment, format) => this.fire(
         'createFormattedDateText',
@@ -1358,12 +1432,12 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         format,
       ),
       getAppointmentDisabled: (appointment) => this._dataAccessors.get('disabled', appointment),
-      onItemContextMenu: that._createActionByOption('onAppointmentContextMenu'),
-      createEventArgs: that._createEventArgs.bind(that),
+      onItemContextMenu: this._createActionByOption('onAppointmentContextMenu'),
+      createEventArgs: this._createEventArgs.bind(this),
 
       newAppointments: Boolean(this.option('_newAppointments')),
       onAppointmentClick: (args: AppointmentClickEvent) => this.actions.onAppointmentClick(args),
-      onListInitialized: (e) => {
+      onListInitialized: (e): void => {
         if (this.option('_newAppointments') && e.element) {
           this.appointmentDragController.createTooltipDraggable(
             $(e.element),
@@ -1373,7 +1447,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
           );
         }
       },
-      onListDisposing: () => {
+      onListDisposing: (): void => {
         this.appointmentDragController.disposeTooltipDraggable();
       },
     } satisfies AppointmentTooltipOptions;
@@ -1383,23 +1457,28 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   _createEventArgs(
     e: ItemContextMenuEvent<AppointmentTooltipItem>,
   ): AppointmentTooltipContextMenuEventArgs {
-    const config: {
+    const itemData = e.itemData?.appointment;
+    if (!itemData) {
+      throw errors.Error('E0001');
+    }
+
+    const eventConfig: {
       itemData: SafeAppointment;
       itemElement: dxElementWrapper;
       targetedAppointment?: SafeAppointment | TargetedAppointment;
     } = {
-      itemData: e.itemData!.appointment,
+      itemData,
       itemElement: $(e.itemElement),
-      targetedAppointment: e.itemData!.targetedAppointment,
+      targetedAppointment: e.itemData?.targetedAppointment,
     };
-    const mappedFields = this.fire('mapAppointmentFields', config) as MappedAppointmentFields;
+    const mappedFields = this.fire('mapAppointmentFields', eventConfig) as MappedAppointmentFields;
 
     return extend({}, mappedFields, {
       component: e.component,
       element: e.element,
       event: e.event,
       model: e.model,
-    });
+    }) as AppointmentTooltipContextMenuEventArgs;
   }
 
   checkAndDeleteAppointment(
@@ -1442,7 +1521,9 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   private initMarkupCore(): void {
     this.readyToRenderAppointments = hasWindow();
 
-    this._workSpace && this.cleanWorkspace();
+    if (this._workSpace) {
+      this.cleanWorkspace();
+    }
 
     this.renderWorkSpace();
     if (this.option('_newAppointments')) {
@@ -1453,7 +1534,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         allDayContainer: this._workSpace.getAllDayContainer(),
       });
     }
-    this.waitAsyncTemplate(() => this.workSpaceRecalculation?.resolve());
+    this.waitAsyncTemplate((): void => { this.workSpaceRecalculation?.resolve(); });
 
     this.createAppointmentDataSource();
     this.setRemoteFilterIfNeeded();
@@ -1462,7 +1543,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   private isDataSourceLoaded(): boolean {
-    return this._dataSource?.isLoaded();
+    return Boolean(this._dataSource?.isLoaded());
   }
 
   _render(): void {
@@ -1495,7 +1576,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       min: this.getViewOption('min'),
       max: this.getViewOption('max'),
       indicatorTime: this.option('indicatorTime'),
-      startViewDate: this.getStartViewDate()!,
+      startViewDate: this.getStartViewDate() ?? new Date(),
       tabIndex: this.option('tabIndex'),
       focusStateEnabled: this.option('focusStateEnabled'),
       useDropDownViewSwitcher: this.option('useDropDownViewSwitcher'),
@@ -1512,7 +1593,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   private appointmentsConfig(): AppointmentCollectionOptions {
-    const config: AppointmentCollectionOptions = {
+    const collectionConfig: AppointmentCollectionOptions = {
       getResourceManager: () => this.resourceManager,
       getAppointmentDataSource: () => this.appointmentDataSource,
       getSortedAppointments: () => this._layoutManager.sortedItems,
@@ -1534,7 +1615,9 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       groups: this.getViewOption('groups'),
       groupByDate: Boolean(this.getViewOption('groupByDate')),
       timeZoneCalculator: this.timeZoneCalculator,
-      getResizableStep: () => (this._workSpace ? this._workSpace.positionHelper.getResizableStep() : 0),
+      getResizableStep: () => (
+        this._workSpace ? this._workSpace.positionHelper.getResizableStep() : 0
+      ),
       getDOMElementsMetaData: () => this._workSpace?.getDOMElementsMetaData(),
       getViewDataProvider: () => this._workSpace?.viewDataProvider,
       // @ts-expect-error protected method
@@ -1545,7 +1628,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       },
     };
 
-    return config;
+    return collectionConfig;
   }
 
   private renderWorkSpace(): void {
@@ -1574,7 +1657,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       Promise.resolve().then(() => {
         this.toggleSmallClass();
         this._workSpace?.updateHeaderEmptyCellWidth();
-      });
+      }).catch(noop);
     }
     const $workSpace = $('<div>').appendTo(this.mainContainer);
 
@@ -1672,7 +1755,11 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       renderAppointments: (): void => { this.renderAppointments(); },
       onShowAllDayPanel: (value: boolean) => this.option('showAllDayPanel', value),
       getHeaderHeight: (): number => utils.DOM.getHeaderHeight(this.header),
-      onScrollEnd: (): void => this._appointments.updateResizableArea(),
+      onScrollEnd: (): void => {
+        if (!this.option('_newAppointments')) {
+          (this._appointments as AppointmentCollection).updateResizableArea();
+        }
+      },
       onInitialized: (e) => {
         if (this.option('_newAppointments')) {
           this.appointmentDragController.createWorkSpaceDraggable(
@@ -1733,7 +1820,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
 
     // @ts-expect-error
-    return this._getTemplateByOption(optionName);
+    return this._getTemplateByOption(optionName) as FunctionTemplate;
   }
 
   private updateOption<T>(viewName: 'workSpace' | 'header', optionName: string, value: T): void {
@@ -1762,7 +1849,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         });
       }
 
-      this.waitAsyncTemplate(() => this.workSpaceRecalculation.resolve());
+      this.waitAsyncTemplate((): void => { this.workSpaceRecalculation.resolve(); });
     }
   }
 
@@ -1812,7 +1899,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
           this.updateAppointmentCore(
             appointmentData,
             newAppointmentData,
-          ).finally(resolve);
+          ).finally(resolve).catch(noop);
         },
         false,
         undefined,
@@ -1863,16 +1950,20 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         }
         this.showRecurrenceChangeConfirm(isDeleted)
           .done((editingMode) => {
-            editingMode === RECURRENCE_EDITING_MODE.SERIES && callback();
-
-            editingMode === RECURRENCE_EDITING_MODE.OCCURRENCE && this.excludeAppointmentFromSeries(
-              rawAppointment,
-              singleAppointment,
-              exceptionDate,
-              isDeleted,
-              Boolean(isPopupEditing),
-              dragEvent,
-            );
+            if (editingMode === RECURRENCE_EDITING_MODE.SERIES) {
+              callback();
+            }
+
+            if (editingMode === RECURRENCE_EDITING_MODE.OCCURRENCE) {
+              this.excludeAppointmentFromSeries(
+                rawAppointment,
+                singleAppointment,
+                exceptionDate,
+                isDeleted,
+                Boolean(isPopupEditing),
+                dragEvent,
+              );
+            }
           })
           .fail(() => {
             if (this.option('_newAppointments')) {
@@ -1909,16 +2000,16 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
     const canCreateNewAppointment = !isDeleted && !isPopupEditing;
     if (canCreateNewAppointment) {
-      this.addAppointment(singleRawAppointment);
+      this.addAppointment(singleRawAppointment).catch(noop);
     }
 
     if (isPopupEditing) {
       this.appointmentPopup.show(singleRawAppointment, {
-        onSave: (newAppointment) => {
-          this.updateAppointment(rawAppointment, appointment.source);
-          return when(this.addAppointment(newAppointment))
-            .done(() => this.scrollToAppointment(newAppointment));
-        },
+        onSave: (newAppointment) => (
+          this.updateAppointment(rawAppointment, appointment.source)
+            .then(() => this.addAppointment(newAppointment as SafeAppointment))
+            .then(() => { this.scrollToAppointment(newAppointment as SafeAppointment); })
+        ),
         title: messageLocalization.format('dxScheduler-editPopupTitle'),
         readOnly: Boolean(appointment.source) && appointment.disabled,
       });
@@ -1926,7 +2017,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     } else {
       this.updateAppointmentCore(rawAppointment, appointment.source, () => {
         this._appointments.moveAppointmentBack(dragEvent);
-      }, dragEvent);
+      }, dragEvent).catch(noop);
     }
   }
 
@@ -1934,7 +2025,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     appointment: SafeAppointment & { recurrenceException?: string },
     exceptionDate: Date,
   ): string {
-    const result: any[] = [];
+    const result: string[] = [];
 
     if (appointment.recurrenceException) {
       result.push(appointment.recurrenceException);
@@ -1946,14 +2037,16 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   private getSerializedDate(date: Date, startDate: Date, isAllDay: boolean): string {
-    isAllDay && date.setHours(
-      startDate.getHours(),
-      startDate.getMinutes(),
-      startDate.getSeconds(),
-      startDate.getMilliseconds(),
-    );
+    if (isAllDay) {
+      date.setHours(
+        startDate.getHours(),
+        startDate.getMinutes(),
+        startDate.getSeconds(),
+        startDate.getMilliseconds(),
+      );
+    }
 
-    return dateSerialization.serializeDate(date, UTC_FULL_DATE_FORMAT);
+    return dateSerialization.serializeDate(date, UTC_FULL_DATE_FORMAT) as string;
   }
 
   private showRecurrenceChangeConfirm(isDeleted: boolean): DeferredObj<string> {
@@ -1968,16 +2061,16 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       showCloseButton: true,
       showTitle: true,
       buttons: [
-        { text: seriesText, onClick() { return RECURRENCE_EDITING_MODE.SERIES; } },
-        { text: occurrenceText, onClick() { return RECURRENCE_EDITING_MODE.OCCURRENCE; } },
+        { text: seriesText, onClick: (): string => RECURRENCE_EDITING_MODE.SERIES },
+        { text: occurrenceText, onClick: (): string => RECURRENCE_EDITING_MODE.OCCURRENCE },
       ],
       popupOptions: {
         wrapperAttr: { class: POPUP_DIALOG_CLASS },
-        onHidden: () => {
+        onHidden: (): void => {
           this._appointments?.focus();
         },
       },
-    } as any);
+    } as CustomDialogOptions) as RecurrenceDialog;
 
     return this.recurrenceDialog.show();
   }
@@ -2015,8 +2108,8 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       appointmentStartDate = resultedStartDate;
     }
 
-    if (!dateUtilsTs.isValidDate(appointmentEndDate)) {
-      appointmentEndDate = cellEndDate!;
+    if (!dateUtilsTs.isValidDate(appointmentEndDate) && cellEndDate) {
+      appointmentEndDate = cellEndDate;
     }
 
     const duration = appointmentEndDate.getTime() - appointmentStartDate.getTime();
@@ -2046,11 +2139,19 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
     let resultedEndDate = new Date(resultedStartDate.getTime() + duration);
 
-    if (this.appointmentTakesAllDay(rawAppointment) && !result.allDay && this._workSpace.supportAllDayRow()) {
+    if (
+      this.appointmentTakesAllDay(rawAppointment)
+      && !result.allDay
+      && this._workSpace.supportAllDayRow()
+    ) {
       resultedEndDate = this._workSpace.calculateEndDate(resultedStartDate);
     }
 
-    if (appointment.allDay && !this._workSpace.supportAllDayRow() && !this._workSpace.keepOriginalHours()) {
+    if (
+      appointment.allDay
+      && !this._workSpace.supportAllDayRow()
+      && !this._workSpace.keepOriginalHours()
+    ) {
       const dateCopy = new Date(resultedStartDate);
       dateCopy.setHours(0);
 
@@ -2071,8 +2172,14 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   // TODO<Appointments>: delete this method when old impl is removed
-  getTargetedAppointment(appointment: SafeAppointment, element: dxElementWrapper): TargetedAppointment {
-    const settings = utils.dataAccessors.getAppointmentSettings(element)!;
+  getTargetedAppointment(
+    appointment: SafeAppointment,
+    element: dxElementWrapper,
+  ): TargetedAppointment {
+    const settings = utils.dataAccessors.getAppointmentSettings(element);
+    if (!settings) {
+      throw errors.Error('E0001');
+    }
     return getTargetedAppointment(
       appointment,
       settings,
@@ -2082,7 +2189,8 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   subscribe<K extends SubscribeKey>(subject: K, action: SubscribeMethods[K]): void {
-    this.subscribes[subject] = subscribes[subject] = action;
+    this.subscribes[subject] = action;
+    subscribes[subject] = action;
   }
 
   fire<Subject extends SubscribeKey>(
@@ -2095,7 +2203,12 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       throw errors.Error('E1031', subject);
     }
 
-    return callback.call(this, ...args);
+    // subscribes callbacks are not fully typed
+    // eslint-disable-next-line @typescript-eslint/no-unsafe-return
+    return (callback as (
+      this: Scheduler,
+      ...callbackArgs: Parameters<SubscribeMethods[Subject]>
+    ) => ReturnType<SubscribeMethods[Subject]>).apply(this, args);
   }
 
   getTargetCellData(): DroppableCellData {
@@ -2114,12 +2227,12 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       cancel: false,
     };
 
-    const performFailAction = function (this: Scheduler, err?: Error): void {
+    const performFailAction = function performFailAction(this: Scheduler, err?: Error): void {
       if (onUpdatePrevented) {
         onUpdatePrevented.call(this);
       }
 
-      if (err && err.name === 'Error') {
+      if (err?.name === 'Error') {
         throw err;
       }
     }.bind(this);
@@ -2134,35 +2247,34 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       this.updatingAppointments.add(target);
     }
 
-    return this.processActionResult(updatingOptions, function (canceled) {
-      let deferred: DeferredObj<void> = Deferred();
-
+    return this.processActionResult(updatingOptions, (canceled) => {
       if (!canceled) {
         this.expandAllDayPanel(rawAppointment);
 
         try {
-          deferred = this.appointmentDataSource
+          return this.appointmentDataSource
             .update(target, rawAppointment)
             .done(() => {
               dragEvent?.cancel.resolve(false);
             })
             .always((storeAppointment) => {
               this.updatingAppointments.delete(target);
-              this.onDataPromiseCompleted(StoreEventNames.UPDATED, storeAppointment);
+              if (isDefined(storeAppointment)) {
+                this.onDataPromiseCompleted(StoreEventNames.UPDATED, storeAppointment);
+              }
             })
-            .fail(() => performFailAction());
+            .fail(() => performFailAction())
+            .then(() => undefined);
         } catch (err: unknown) {
           performFailAction(err instanceof Error ? err : undefined);
           this.updatingAppointments.delete(target);
-          deferred.resolve();
+          return Deferred<void>().resolve().promise();
         }
-      } else {
-        performFailAction();
-        this.updatingAppointments.delete(target);
-        deferred.resolve();
       }
 
-      return deferred.promise();
+      performFailAction();
+      this.updatingAppointments.delete(target);
+      return Deferred<void>().resolve().promise();
     });
   }
 
@@ -2178,10 +2290,11 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
     if (isPromise(actionOptions.cancel)) {
       when(fromPromise(actionOptions.cancel)).always((cancel) => {
-        if (!isDefined(cancel)) {
-          cancel = (actionOptions.cancel as DeferredObj<boolean>).state() === 'rejected';
+        let isCanceled = cancel;
+        if (!isDefined(isCanceled)) {
+          isCanceled = (actionOptions.cancel as DeferredObj<boolean>).state() === 'rejected';
         }
-        resolveCallback(callback.call(this, cancel));
+        resolveCallback(callback.call(this, isCanceled));
       });
     } else {
       resolveCallback(callback.call(this, actionOptions.cancel as boolean));
@@ -2201,20 +2314,23 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     storeAppointment: SafeAppointment | Error,
     appointment?: SafeAppointment,
   ): void {
-    const args: any = { appointmentData: appointment || storeAppointment };
+    const args: AppointmentCompletedOptions = {
+      appointmentData: (appointment ?? storeAppointment) as SafeAppointment,
+    };
 
     if (storeAppointment instanceof Error) {
       args.error = storeAppointment;
-    } else {
-      this.appointmentPopup.visible && this.appointmentPopup.hide();
+    } else if (this.appointmentPopup.visible) {
+      this.appointmentPopup.hide();
     }
 
-    this.actions[handlerName](args);
+    const handler = this.actions[handlerName] as (args: AppointmentCompletedOptions) => void;
+    handler(args);
     this._fireContentReadyAction();
   }
 
   getAppointmentsInstance(): Appointments | AppointmentCollection {
-    return this._appointments;
+    return this._appointments as Appointments | AppointmentCollection;
   }
 
   getLayoutManager(): AppointmentLayoutManager {
@@ -2237,7 +2353,11 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     );
   }
 
-  dayHasAppointment(day: Date, rawAppointment: SafeAppointment | Appointment, trimTime: boolean): boolean {
+  dayHasAppointment(
+    day: Date,
+    rawAppointment: SafeAppointment | Appointment,
+    trimTime: boolean,
+  ): boolean {
     const getConvertedToTimeZone = (date: Date): Date => this.timeZoneCalculator.createDate(date, 'toGrid');
 
     const appointment = new AppointmentAdapter(
@@ -2255,15 +2375,19 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       return startDate.getTime() === endDate.getTime();
     }
 
+    let dayStart = day;
+    let startDateStart = startDate;
+    let endDateEnd = endDate;
+
     if (trimTime) {
-      day = dateUtils.trimTime(day);
-      startDate = dateUtils.trimTime(startDate);
-      endDate = dateUtils.trimTime(endDate);
+      dayStart = dateUtils.trimTime(day);
+      startDateStart = dateUtils.trimTime(startDate);
+      endDateEnd = dateUtils.trimTime(endDate);
     }
 
-    const dayTimeStamp = day.getTime();
-    const startDateTimeStamp = startDate.getTime();
-    const endDateTimeStamp = endDate.getTime();
+    const dayTimeStamp = dayStart.getTime();
+    const startDateTimeStamp = startDateStart.getTime();
+    const endDateTimeStamp = endDateEnd.getTime();
 
     return startDateTimeStamp <= dayTimeStamp && dayTimeStamp <= endDateTimeStamp;
   }
@@ -2310,15 +2434,21 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       delete this.editAppointmentData; // TODO
       if (this.editing.allowAdding) {
         this.appointmentPopup.show(appointmentData, {
-          onSave: (appointment) => when(this.addAppointment(appointment))
-            .done(() => this.scrollToAppointment(appointment)),
+          onSave: (appointment) => (
+            this.addAppointment(appointment as SafeAppointment)
+              .then(() => { this.scrollToAppointment(appointment as SafeAppointment); })
+          ),
           title: messageLocalization.format('dxScheduler-newPopupTitle'),
           readOnly: false,
         });
       }
     } else {
       const appointmentData = rawAppointment as SafeAppointment;
-      const newTargetedAppointment = extend({}, appointmentData, newRawTargetedAppointment) as SafeAppointment;
+      const newTargetedAppointment = extend(
+        {},
+        appointmentData,
+        newRawTargetedAppointment,
+      ) as SafeAppointment;
       const startDate = this._dataAccessors.get(
         'startDate',
         Object.keys(newRawTargetedAppointment).length ? newRawTargetedAppointment : appointmentData,
@@ -2332,8 +2462,10 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         const readOnly = isDisabled || !this.editing.allowUpdating;
 
         this.appointmentPopup.show(appointmentData, {
-          onSave: (appointment) => when(this.updateAppointment(appointmentData, appointment))
-            .done(() => this.scrollToAppointment(appointment)),
+          onSave: (appointment) => (
+            this.updateAppointment(appointmentData, appointment as SafeAppointment)
+              .then(() => { this.scrollToAppointment(appointment as SafeAppointment); })
+          ),
           title: messageLocalization.format('dxScheduler-editPopupTitle'),
           readOnly,
         });
@@ -2343,10 +2475,10 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
   createPopupAppointment(): SafeAppointment {
     const result: SafeAppointment = {};
-    const toMs = dateUtils.dateToMilliseconds;
+    const msPerMinute = dateUtils.dateToMilliseconds('minute');
 
     const startDate = new Date(this.option('currentDate'));
-    const endDate = new Date(startDate.getTime() + this.option('cellDuration') * toMs('minute'));
+    const endDate = new Date(startDate.getTime() + this.option('cellDuration') * msPerMinute);
 
     this._dataAccessors.set('startDate', result, startDate);
     this._dataAccessors.set('endDate', result, endDate);
@@ -2356,7 +2488,9 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
   hideAppointmentPopup(saveChanges?: boolean): void {
     if (this.appointmentPopup?.visible) {
-      saveChanges && this.appointmentPopup.saveChangesAsync();
+      if (saveChanges) {
+        this.appointmentPopup.saveChangesAsync().catch(noop);
+      }
       this.appointmentPopup.hide();
     }
   }
@@ -2368,17 +2502,21 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     targetedAppointment?: SafeAppointment,
   ): void {
     if (appointment) {
-      const settings: any = utils.dataAccessors.getAppointmentSettings(element);
+      const settings = utils.dataAccessors.getAppointmentSettings(element);
+      if (!settings) {
+        return;
+      }
+
       const appointmentConfig = {
         itemData: targetedAppointment ?? appointment,
-        groupIndex: settings?.groupIndex,
+        groupIndex: settings.groupIndex ?? 0,
       };
 
       const info: AppointmentTooltipItem = {
         appointment,
         targetedAppointment,
         color: this.resourceManager.getAppointmentColor(appointmentConfig),
-        settings,
+        settings: settings as AppointmentItemViewModel,
       };
 
       this.showAppointmentTooltipCore(element, [info]);
@@ -2406,11 +2544,13 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       this.hideAppointmentTooltip();
     } else {
       this.processActionResult({ ...arg, cancel: arg.cancel ?? false }, (canceled) => {
-        !canceled && this.appointmentTooltip.show(target, data, {
-          ...this.getExtraAppointmentTooltipOptions(),
-          ...options,
-        });
-      });
+        if (!canceled) {
+          this.appointmentTooltip.show(target, data, {
+            ...this.getExtraAppointmentTooltipOptions(),
+            ...options,
+          });
+        }
+      }).catch(noop);
     }
   }
 
@@ -2423,29 +2563,39 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     groupValuesOrOptions?: ScrollToGroupValuesOrOptions,
     allDay?: boolean | undefined,
   ): void {
-    let groupValues;
-    let allDayValue;
-    let align: 'start' | 'center' = 'center';
-
     if (this.isScrollOptionsObject(groupValuesOrOptions)) {
-      groupValues = groupValuesOrOptions.group;
-      allDayValue = groupValuesOrOptions.allDay;
-      align = groupValuesOrOptions.alignInView ?? 'center';
-    } else {
-      if (isDefined(groupValuesOrOptions) || isDefined(allDay)) {
-        errors.log('W0002', 'dxScheduler', 'scrollTo(date, group, allDay)', '26.1', 'Use scrollTo(date, { group, allDay, alignInView }) instead.');
-      }
+      this._workSpace.scrollTo(
+        date,
+        groupValuesOrOptions.group,
+        groupValuesOrOptions.allDay,
+        true,
+        groupValuesOrOptions.alignInView ?? 'center',
+      );
+      return;
+    }
 
-      groupValues = groupValuesOrOptions;
-      allDayValue = allDay;
+    if (isDefined(groupValuesOrOptions) || isDefined(allDay)) {
+      errors.log(
+        'W0002',
+        'dxScheduler',
+        'scrollTo(date, group, allDay)',
+        '26.1',
+        'Use scrollTo(date, { group, allDay, alignInView }) instead.',
+      );
     }
 
-    this._workSpace.scrollTo(date, groupValues, allDayValue, true, align);
+    this._workSpace.scrollTo(date, groupValuesOrOptions, allDay, true, 'center');
   }
 
-  private isScrollOptionsObject(options?: ScrollToGroupValuesOrOptions): options is ScrollToOptions {
+  private isScrollOptionsObject(
+    options?: ScrollToGroupValuesOrOptions,
+  ): options is ScrollToOptions {
     return Boolean(options) && typeof options === 'object'
-      && ('alignInView' in options || 'allDay' in options || 'group' in options);
+      && (
+        'alignInView' in options
+        || 'allDay' in options
+        || 'group' in options
+      );
   }
 
   private isHorizontalVirtualScrolling(): boolean {
@@ -2483,7 +2633,9 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
       return this.appointmentDataSource
         .add(serializedAppointment)
-        .always((storeAppointment) => this.onDataPromiseCompleted(StoreEventNames.ADDED, storeAppointment));
+        .always((storeAppointment) => {
+          this.onDataPromiseCompleted(StoreEventNames.ADDED, storeAppointment);
+        });
     });
   }
 
@@ -2515,17 +2667,21 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     rawAppointment: SafeAppointment,
     deletingOptions: AppointmentDeletingOptions,
   ): void {
-    this.processActionResult(deletingOptions, function (canceled) {
+    this.processActionResult(deletingOptions, (canceled) => {
       if (!canceled) {
         this.appointmentDataSource
           .remove(rawAppointment)
-          .always((storeAppointment) => this.onDataPromiseCompleted(
-            StoreEventNames.DELETED,
-            storeAppointment,
-            rawAppointment,
-          ));
+          .always((storeAppointment) => {
+            if (isDefined(storeAppointment)) {
+              this.onDataPromiseCompleted(
+                StoreEventNames.DELETED,
+                storeAppointment,
+                rawAppointment,
+              );
+            }
+          });
       }
-    });
+    }).catch(noop);
   }
 
   deleteRecurrence(
@@ -2533,13 +2689,11 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     date: Date | string,
     recurrenceEditMode: RecurrenceEditMode,
   ): void {
-    if (typeof date === 'string') {
-      date = new Date(date);
-    }
+    const dateValue = typeof date === 'string' ? new Date(date) : date;
     this.checkRecurringAppointment(
       appointment,
       {},
-      date,
+      dateValue,
       () => {
         this.processDeleteAppointment(
           appointment,
@@ -2608,6 +2762,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 }
 
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
 (Scheduler as any).include(DataHelperMixin);
 
 // @ts-ignore

From c02ca1f6171ea7d539ffebc119de87b50edac3ed Mon Sep 17 00:00:00 2001
From: Sergei Burkatskii <noreply@github.com>
Date: Wed, 24 Jun 2026 10:45:05 +0200
Subject: [PATCH 11/17] fix: fix build

---
 .../m_compact_appointments_helper.ts          |   3 +-
 .../js/__internal/scheduler/m_scheduler.ts    | 152 ++++++++++++++----
 .../view_model/common/get_compare_options.ts  |   2 +-
 3 files changed, 119 insertions(+), 38 deletions(-)

diff --git a/packages/devextreme/js/__internal/scheduler/m_compact_appointments_helper.ts b/packages/devextreme/js/__internal/scheduler/m_compact_appointments_helper.ts
index dcbf80a8e1b8..d7b142f78d6a 100644
--- a/packages/devextreme/js/__internal/scheduler/m_compact_appointments_helper.ts
+++ b/packages/devextreme/js/__internal/scheduler/m_compact_appointments_helper.ts
@@ -91,7 +91,7 @@ export class CompactAppointmentsHelper {
         getItemSettings,
       };
 
-      workSpace.createDragBehaviorBase($element, $schedulerElement, options);
+      workSpace?.createDragBehaviorBase($element, $schedulerElement, options);
     };
   }
 
@@ -105,7 +105,6 @@ export class CompactAppointmentsHelper {
   private createCompactButton(template, options: CompactAppointmentOptions) {
     const $button = this.createCompactButtonElement(options);
 
-    // @ts-expect-error
     return this.instance._createComponent($button, Button, {
       type: 'default',
       width: options.width,
diff --git a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
index ec6f956a02d6..baea00b95faf 100644
--- a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
+++ b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
@@ -1,4 +1,3 @@
-/* eslint-disable devextreme-custom/no-deferred */
 import { triggerResizeEvent } from '@js/common/core/events/visibility_change';
 import dateLocalization from '@js/common/core/localization/date';
 import messageLocalization from '@js/common/core/localization/message';
@@ -63,7 +62,7 @@ import type Scrollable from '@ts/ui/scroll_view/scrollable';
 
 import { createA11yStatusContainer } from './a11y_status/a11y_status_render';
 import { getA11yStatusText } from './a11y_status/a11y_status_text';
-import { AppointmentDragController } from './appointment_drag_controller';
+import { AppointmentDragController, type WorkSpaceDraggableOptions } from './appointment_drag_controller';
 import type { AppointmentFormConfig } from './appointment_popup/form';
 import { AppointmentForm } from './appointment_popup/form';
 import { AppointmentPopup } from './appointment_popup/popup';
@@ -97,6 +96,8 @@ import type {
   AppointmentTooltipContextMenuEventArgs,
   AppointmentTooltipItem,
   CreateComponentFn,
+  DOMMetaData,
+  GroupBoundsOffset,
   MappedAppointmentFields,
   SafeAppointment,
   ScrollToGroupValuesOrOptions, ScrollToOptions, TargetedAppointment,
@@ -117,14 +118,15 @@ import { ResourceManager } from './utils/resource_manager/resource_manager';
 import type { GroupValues } from './utils/resource_manager/types';
 import timeZoneUtils, { type TimezoneLabel } from './utils_time_zone';
 import AppointmentLayoutManager from './view_model/appointments_layout_manager';
+import type { CollectorCSS, RealSize } from './view_model/generate_view_model/steps/add_geometry/types';
 import { AppointmentDataSource } from './view_model/m_appointment_data_source';
-import type { AppointmentViewModelPlain, AppointmentItemViewModel } from './view_model/types';
+import type { AppointmentItemViewModel, AppointmentViewModelPlain, PanelName } from './view_model/types';
 import SchedulerAgenda from './workspaces/agenda';
 import SchedulerTimelineDay from './workspaces/timeline_day';
 import SchedulerTimelineMonth from './workspaces/timeline_month';
 import SchedulerTimelineWeek from './workspaces/timeline_week';
-import type SchedulerWorkSpace from './workspaces/work_space';
-import type { DroppableCellData, WorkspaceOptionsInternal } from './workspaces/work_space';
+import type ViewDataProvider from './workspaces/view_model/view_data_provider';
+import type { WorkspaceOptionsInternal } from './workspaces/work_space';
 import SchedulerWorkSpaceDay from './workspaces/work_space_day';
 import SchedulerWorkSpaceMonth from './workspaces/work_space_month';
 import SchedulerWorkSpaceWeek from './workspaces/work_space_week';
@@ -199,6 +201,93 @@ const RECURRENCE_EDITING_MODE = {
   CANCEL: 'cancel',
 };
 
+type DroppableCellData = Pick<ViewCellData, 'startDate' | 'endDate' | 'allDay' | 'groups'>;
+
+interface WorkSpaceCoordinates {
+  top: number;
+  left: number;
+  groupIndex?: number;
+}
+
+interface WorkSpacePositionHelper {
+  getResizableStep: () => number;
+  getHorizontalMax: (groupIndex: number) => number;
+  getVerticalMax: (options: {
+    groupIndex: number;
+    isVirtualScrolling: boolean;
+    showAllDayPanel: boolean;
+    supportAllDayRow: boolean;
+    isGroupedAllDayPanel: boolean;
+    isVerticalGrouping: boolean;
+  }) => number;
+}
+
+interface VirtualScrollingDispatcherLike {
+  cellCountInsideLeftVirtualCell: number;
+  cellCountInsideRightVirtualCell: number;
+  cellCountInsideTopVirtualRow: number;
+}
+
+interface SchedulerWorkSpaceLike {
+  type: ViewType;
+  NAME?: string;
+  dragBehavior: AppointmentDragBehavior | null;
+  positionHelper: WorkSpacePositionHelper;
+  virtualScrollingDispatcher: VirtualScrollingDispatcherLike;
+  viewDataProvider: ViewDataProvider;
+  option: (name: string | Record<string, unknown>, value?: unknown) => unknown;
+  getDateRange: () => Date[];
+  getCellFromDragTarget: ($dragTarget: dxElementWrapper) => dxElementWrapper | null;
+  renderAgendaLayout?: (viewModel: AppointmentViewModelPlain[]) => void;
+  calculateEndDate: (startDate: Date) => Date;
+  updateScrollPosition: (date: Date, groupValues: GroupValues, inAllDayRow: boolean) => void;
+  supportAllDayRow: () => boolean;
+  getAllDayContainer: () => dxElementWrapper | null;
+  getFixedContainer: () => dxElementWrapper;
+  getDOMElementsMetaData: () => DOMMetaData;
+  isVerticalGroupedWorkSpace: () => boolean;
+  isVirtualScrolling: () => boolean;
+  isGroupedByDate: () => boolean;
+  needRecalculateResizableArea: () => boolean;
+  getHeaderDate: () => Date;
+  updateHeaderEmptyCellWidth: () => void;
+  initDragBehavior: (scheduler: unknown) => void;
+  attachTablesEvents: () => void;
+  getWorkArea: () => dxElementWrapper;
+  $element: () => dxElementWrapper;
+  renderCurrentDateTimeLineAndShader: () => void;
+  _dispose: () => void;
+  _dimensionChanged: () => void;
+  getScrollable: () => Scrollable;
+  getScrollableContainer: () => dxElementWrapper;
+  getCellData: ($cell: dxElementWrapper) => DroppableCellData;
+  getCellWidth: () => number;
+  getCellHeight: () => number;
+  getGroupCount: () => number;
+  getGroupBounds: (coordinates: WorkSpaceCoordinates) => GroupBoundsOffset | undefined;
+  getPanelDOMSize: (panelName: PanelName) => RealSize;
+  getCollectorDimension: (isCompactCollector: boolean, panelName: PanelName) => CollectorCSS;
+  getAgendaVerticalStepHeight: () => number;
+  createDragBehaviorBase: (
+    targetElement: dxElementWrapper,
+    rootElement: dxElementWrapper,
+    options: Record<string, unknown>,
+  ) => void;
+  removeDroppableCellClass: () => void;
+  keepOriginalHours: () => boolean;
+  getDataByDroppableCell: () => DroppableCellData;
+  getStartViewDate: () => Date | undefined;
+  getEndViewDate: () => Date;
+  scrollTo: (
+    date: Date,
+    groupValuesOrOptions?: ScrollToGroupValuesOrOptions,
+    allDay?: boolean,
+    throwWarning?: boolean,
+    align?: 'start' | 'center',
+  ) => void;
+  focus: () => void;
+}
+
 type SchedulerActionCancel = boolean | PromiseLike<boolean> | DeferredObj<boolean | undefined>;
 
 type SchedulerActionOptions = {
@@ -280,15 +369,14 @@ type AppointmentsEditingOptions = Partial<{
 }>;
 
 interface SchedulerAppointmentsHost {
-  option(options: Record<string, unknown>): unknown;
-  option(name: string, value?: unknown): unknown;
-  repaint(): void;
-  $element(): dxElementWrapper;
-  focus(): void;
-  moveAppointmentBack(dragEvent?: SchedulerDragEvent | null): void;
-  updateResizableArea(): void;
-  renderDragClone(...args: unknown[]): dxElementWrapper;
-  getAppointmentData(...args: unknown[]): unknown;
+  option: ((options: Record<string, unknown>) => unknown) & ((name: string, value?: unknown) => unknown);
+  repaint: () => void;
+  $element: () => dxElementWrapper;
+  focus: () => void;
+  moveAppointmentBack: (dragEvent?: SchedulerDragEvent | null) => void;
+  updateResizableArea: () => void;
+  renderDragClone: (...args: unknown[]) => dxElementWrapper;
+  getAppointmentData: (...args: unknown[]) => unknown;
 }
 
 class Scheduler extends SchedulerOptionsBaseWidget {
@@ -306,7 +394,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
   // TODO: used externally in m_appointment_drag_behavior.ts,
   // m_subscribes.ts, workspaces/work_space.ts
-  _workSpace!: SchedulerWorkSpace;
+  _workSpace!: SchedulerWorkSpaceLike;
 
   private header?: SchedulerHeader;
 
@@ -321,6 +409,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   declare _dataSource: DataSource | undefined;
 
   // TODO: used externally in workspaces/work_space.ts
+  // eslint-disable-next-line @typescript-eslint/naming-convention -- inherited Widget API
   declare _createComponent: CreateComponentFn;
 
   // TODO: used externally in m_subscribes.ts,
@@ -830,7 +919,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     const result: DeferredObj<void> = Deferred();
 
     if (this._dataSource) {
-      void this._dataSource.load().then(() => {
+      this._dataSource.load().then(() => {
         hideLoading().catch(noop);
 
         this._fireContentReadyAction(result);
@@ -1121,7 +1210,6 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.appointmentDataSource.cleanState();
 
     if (this.isAgenda()) {
-      // @ts-expect-error renderAgendaLayout exists only on agenda workspace
       this._workSpace.renderAgendaLayout?.(viewModel);
     }
   }
@@ -1349,7 +1437,6 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       resourceManager: this.resourceManager,
       firstDayOfWeek: this.getFirstDayOfWeek(),
       startDayHour: this.option('startDayHour') ?? 0,
-      // @ts-expect-error
       createComponent: this._createComponent.bind(this),
       getCalculatedEndDate: (startDateWithStartHour: Date): Date => (
         this._workSpace.calculateEndDate(startDateWithStartHour)
@@ -1362,7 +1449,6 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   createAppointmentPopup(form: AppointmentForm): AppointmentPopup {
     const scheduler = {
       getElement: (): dxElementWrapper => this.$element(),
-      // @ts-expect-error
       createComponent: this._createComponent.bind(this),
       focus: (): void => { this.focus(); },
 
@@ -1415,8 +1501,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
   private getAppointmentTooltipOptions(): AppointmentTooltipOptions {
     return {
-      // @ts-expect-error _createComponent is not defined in ts
-      createComponent: this._createComponent.bind(this),
+      createComponent: this._createComponent.bind(this) as AppointmentTooltipOptions['createComponent'],
       container: this.$element(),
       getScrollableContainer: this.getWorkSpaceScrollableContainer.bind(this),
       addDefaultTemplates: this._templateManager.addDefaultTemplates.bind(this._templateManager),
@@ -1562,7 +1647,6 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     if (isHeaderShown) {
       const $header = $('<div>').appendTo(this.mainContainer);
       const headerOptions = this.headerConfig();
-      // @ts-expect-error
       this.header = this._createComponent($header, SchedulerHeader, headerOptions);
     }
   }
@@ -1620,7 +1704,6 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       ),
       getDOMElementsMetaData: () => this._workSpace?.getDOMElementsMetaData(),
       getViewDataProvider: () => this._workSpace?.viewDataProvider,
-      // @ts-expect-error protected method
       isVerticalGroupedWorkSpace: () => this._workSpace.isVerticalGroupedWorkSpace(),
       isDateAndTimeView: () => isDateAndTimeView(this._workSpace.type),
       onContentReady: () => {
@@ -1645,7 +1728,6 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
     this.recalculateWorkspace();
     if (currentViewOptions.startDate) {
-      // @ts-expect-error protected method
       this.updateOption('header', 'currentDate', this._workSpace.getHeaderDate());
     }
   }
@@ -1665,14 +1747,13 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     const workSpaceComponent = VIEWS_CONFIG[currentViewType].workSpace;
     const workSpaceConfig = this.workSpaceConfig(this.currentView);
     // @ts-expect-error
-    this._workSpace = this._createComponent($workSpace, workSpaceComponent, workSpaceConfig);
+    this._workSpace = this._createComponent($workSpace, workSpaceComponent, workSpaceConfig) as SchedulerWorkSpaceLike;
 
     if (!this.option('_newAppointments')) {
       if (this.allowDragging()) {
         this._workSpace.initDragBehavior(this);
       }
     }
-    // @ts-expect-error protected method
     this._workSpace.attachTablesEvents();
     this._workSpace.getWorkArea().append(this._appointments.$element());
   }
@@ -1682,7 +1763,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     const workSpaceConfig = this.workSpaceConfig(this.currentView);
     const workSpaceComponent = VIEWS_CONFIG.agenda.workSpace;
     // @ts-expect-error
-    this._workSpace = this._createComponent($workSpace, workSpaceComponent, workSpaceConfig);
+    this._workSpace = this._createComponent($workSpace, workSpaceComponent, workSpaceConfig) as SchedulerWorkSpaceLike;
     this._workSpace.getWorkArea().append(this._appointments.$element());
   }
 
@@ -1691,7 +1772,6 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.workSpaceRecalculation = new Deferred();
     triggerResizeEvent(this._workSpace.$element());
     this.waitAsyncTemplate(() => {
-      // @ts-expect-error protected method
       this._workSpace.renderCurrentDateTimeLineAndShader();
     });
   }
@@ -1757,7 +1837,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       getHeaderHeight: (): number => utils.DOM.getHeaderHeight(this.header),
       onScrollEnd: (): void => {
         if (!this.option('_newAppointments')) {
-          (this._appointments as AppointmentCollection).updateResizableArea();
+          (this._appointments as unknown as AppointmentCollection).updateResizableArea();
         }
       },
       onInitialized: (e) => {
@@ -1765,7 +1845,9 @@ class Scheduler extends SchedulerOptionsBaseWidget {
           this.appointmentDragController.createWorkSpaceDraggable(
             $(e.element),
             {
-              getAppointmentData: this._appointments.getAppointmentData.bind(this._appointments),
+              getAppointmentData: this._appointments.getAppointmentData.bind(
+                this._appointments,
+              ) as WorkSpaceDraggableOptions['getAppointmentData'],
             },
           );
         }
@@ -1869,7 +1951,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this._workSpace.getScrollableContainer();
   }
 
-  getWorkSpace(): SchedulerWorkSpace | undefined {
+  getWorkSpace(): SchedulerWorkSpaceLike {
     return this._workSpace;
   }
 
@@ -2268,13 +2350,13 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         } catch (err: unknown) {
           performFailAction(err instanceof Error ? err : undefined);
           this.updatingAppointments.delete(target);
-          return Deferred<void>().resolve().promise();
+          return Deferred().resolve().promise();
         }
       }
 
       performFailAction();
       this.updatingAppointments.delete(target);
-      return Deferred<void>().resolve().promise();
+      return Deferred().resolve().promise();
     });
   }
 
@@ -2330,7 +2412,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   getAppointmentsInstance(): Appointments | AppointmentCollection {
-    return this._appointments as Appointments | AppointmentCollection;
+    return this._appointments as unknown as Appointments | AppointmentCollection;
   }
 
   getLayoutManager(): AppointmentLayoutManager {
@@ -2726,7 +2808,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   private validateKeyFieldIfAgendaExist(): void {
-    if (!this.appointmentDataSource.isDataSourceInit) {
+    if (!this.appointmentDataSource?.isDataSourceInit) {
       return;
     }
 
diff --git a/packages/devextreme/js/__internal/scheduler/view_model/common/get_compare_options.ts b/packages/devextreme/js/__internal/scheduler/view_model/common/get_compare_options.ts
index 6fbd9b9b0391..f6c0a4e628fe 100644
--- a/packages/devextreme/js/__internal/scheduler/view_model/common/get_compare_options.ts
+++ b/packages/devextreme/js/__internal/scheduler/view_model/common/get_compare_options.ts
@@ -6,7 +6,7 @@ export const getCompareOptions = (
   schedulerStore: Scheduler,
 ): CompareOptions => {
   const workspace = schedulerStore.getWorkSpace();
-  const dateRange = workspace.getDateRange() as Date[];
+  const dateRange = workspace.getDateRange();
   const compareOptions = {
     startDayHour: schedulerStore.getViewOption('startDayHour'),
     endDayHour: schedulerStore.getViewOption('endDayHour'),

From c5340fb7f7ba50ea5b105c55006bf79a7e346278 Mon Sep 17 00:00:00 2001
From: Sergei Burkatskii <noreply@github.com>
Date: Wed, 24 Jun 2026 12:23:54 +0200
Subject: [PATCH 12/17] fix: fix tests

---
 .../js/__internal/scheduler/m_scheduler.ts    | 54 +++++++++++++------
 .../scheduler/workspaces/work_space.ts        |  2 +
 2 files changed, 41 insertions(+), 15 deletions(-)

diff --git a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
index baea00b95faf..5f4e75c0258e 100644
--- a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
+++ b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
@@ -377,6 +377,17 @@ interface SchedulerAppointmentsHost {
   updateResizableArea: () => void;
   renderDragClone: (...args: unknown[]) => dxElementWrapper;
   getAppointmentData: (...args: unknown[]) => unknown;
+  // eslint-disable-next-line @typescript-eslint/naming-convention
+  _createComponent: CreateComponentFn;
+  _renderItem: (index: number, item: unknown, container?: dxElementWrapper) => dxElementWrapper;
+  // eslint-disable-next-line @typescript-eslint/naming-convention
+  _getItemData: (element: dxElementWrapper) => unknown;
+  notifyObserver: (subject: string, args?: unknown) => void;
+  invoke: (funcName: string, ...args: unknown[]) => unknown;
+  // eslint-disable-next-line @typescript-eslint/naming-convention
+  _setDragSourceAppointment: (appointment: unknown, settings: unknown) => void;
+  // eslint-disable-next-line @typescript-eslint/naming-convention
+  _removeDragSourceClassFromDraggedAppointment: () => void;
 }
 
 class Scheduler extends SchedulerOptionsBaseWidget {
@@ -481,7 +492,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     const whenLoaded = this.postponedOperations.add('loadResources', () => {
       const groups = this.getViewOption('groups');
 
-      return when(this.resourceManager.loadGroupResources(groups, forceReload));
+      return fromPromise(this.resourceManager.loadGroupResources(groups, forceReload));
     }, undefined);
 
     const resolveCallbacks: DeferredObj<void> = Deferred();
@@ -507,6 +518,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       case 'firstDayOfWeek':
         this.updateOption('workSpace', name, value);
         this.updateOption('header', name, value);
+        this.updateOption('header', 'startViewDate', this.getStartViewDate());
         this.createAppointmentPopupForm();
         break;
       case 'currentDate': {
@@ -527,7 +539,11 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
         this.postponeResourceLoading().done(() => {
           if (this._dataSource) {
-            this.appointmentDataSource.setDataSource(this._dataSource);
+            if (this.appointmentDataSource) {
+              this.appointmentDataSource.setDataSource(this._dataSource);
+            } else {
+              this.createAppointmentDataSource();
+            }
           }
           this.setRemoteFilterIfNeeded();
           this.updateOption('workSpace', 'showAllDayPanel', this.option('showAllDayPanel'));
@@ -932,7 +948,8 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         showLoading({
           container: this.$element().get(0),
           position: {
-            of: this.$element().get(0),
+            // @ts-expect-error
+            of: this.$element(),
           },
         }).catch(noop);
       }
@@ -1207,7 +1224,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       : [];
 
     this._appointments.option('items', viewModel);
-    this.appointmentDataSource.cleanState();
+    this.appointmentDataSource?.cleanState();
 
     if (this.isAgenda()) {
       this._workSpace.renderAgendaLayout?.(viewModel);
@@ -1660,7 +1677,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       min: this.getViewOption('min'),
       max: this.getViewOption('max'),
       indicatorTime: this.option('indicatorTime'),
-      startViewDate: this.getStartViewDate() ?? new Date(),
+      startViewDate: this.getStartViewDate() ?? this.getViewOption('currentDate'),
       tabIndex: this.option('tabIndex'),
       focusStateEnabled: this.option('focusStateEnabled'),
       useDropDownViewSwitcher: this.option('useDropDownViewSwitcher'),
@@ -1727,6 +1744,14 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
 
     this.recalculateWorkspace();
+
+    if (this.header) {
+      const startViewDate = this.getStartViewDate();
+      if (startViewDate) {
+        this.updateOption('header', 'startViewDate', startViewDate);
+      }
+    }
+
     if (currentViewOptions.startDate) {
       this.updateOption('header', 'currentDate', this._workSpace.getHeaderDate());
     }
@@ -1777,7 +1802,6 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   }
 
   private workSpaceConfig(currentViewOptions: NormalizedView): WorkspaceOptionsInternal {
-    const cellDuration = this.option('cellDuration');
     const scrolling = this.getViewOption('scrolling');
     const isVirtualScrolling = scrolling.mode === 'virtual';
     const horizontalVirtualScrollingAllowed = isVirtualScrolling
@@ -1805,7 +1829,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       focusStateEnabled: Boolean(this.option('focusStateEnabled')),
       showAllDayPanel: this.option('showAllDayPanel'),
       showCurrentTimeIndicator: this.option('showCurrentTimeIndicator'),
-      indicatorTime: this.option('indicatorTime') ?? new Date(),
+      indicatorTime: this.option('indicatorTime'),
       indicatorUpdateInterval: this.option('indicatorUpdateInterval'),
       shadeUntilCurrentTime: this.option('shadeUntilCurrentTime'),
       crossScrollingEnabled,
@@ -1858,11 +1882,13 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         }
       },
       rtlEnabled: Boolean(this.option('rtlEnabled')),
-      hoursInterval: cellDuration / 60,
+      cellDuration: this.option('cellDuration'),
       allDayExpanded: false,
       currentDate: this.getViewOption('currentDate'),
     }, currentViewOptions) as WorkspaceOptionsInternal;
 
+    workSpaceOptions.hoursInterval = workSpaceOptions.cellDuration / 60;
+
     workSpaceOptions.notifyScheduler = this.notifyScheduler;
     workSpaceOptions.groups = this.resourceManager.groupResources();
     workSpaceOptions.onCellClick = this._createActionByOption('onCellClick') as (e: CellClickEvent) => void;
@@ -1981,7 +2007,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
           this.updateAppointmentCore(
             appointmentData,
             newAppointmentData,
-          ).finally(resolve).catch(noop);
+          ).then(resolve);
         },
         false,
         undefined,
@@ -2585,13 +2611,10 @@ class Scheduler extends SchedulerOptionsBaseWidget {
   ): void {
     if (appointment) {
       const settings = utils.dataAccessors.getAppointmentSettings(element);
-      if (!settings) {
-        return;
-      }
 
       const appointmentConfig = {
         itemData: targetedAppointment ?? appointment,
-        groupIndex: settings.groupIndex ?? 0,
+        groupIndex: settings?.groupIndex ?? 0,
       };
 
       const info: AppointmentTooltipItem = {
@@ -2625,14 +2648,15 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     if (this.appointmentTooltip.isShownForTarget(target)) {
       this.hideAppointmentTooltip();
     } else {
-      this.processActionResult({ ...arg, cancel: arg.cancel ?? false }, (canceled) => {
+      // @ts-expect-error
+      this.processActionResult(arg, (canceled) => {
         if (!canceled) {
           this.appointmentTooltip.show(target, data, {
             ...this.getExtraAppointmentTooltipOptions(),
             ...options,
           });
         }
-      }).catch(noop);
+      });
     }
   }
 
diff --git a/packages/devextreme/js/__internal/scheduler/workspaces/work_space.ts b/packages/devextreme/js/__internal/scheduler/workspaces/work_space.ts
index 6e839a9a16fe..6a04f340bcd2 100644
--- a/packages/devextreme/js/__internal/scheduler/workspaces/work_space.ts
+++ b/packages/devextreme/js/__internal/scheduler/workspaces/work_space.ts
@@ -319,6 +319,7 @@ export interface WorkspaceOptionsInternal extends WidgetProperties<SchedulerWork
   onCellClick: ((e: CellClickEvent) => void) | undefined;
   onCellContextMenu: ((e: CellContextMenuEvent) => void) | undefined;
   currentDate: Date;
+  cellDuration: number;
   hoursInterval: number;
   allDayExpanded: boolean;
 
@@ -2620,6 +2621,7 @@ class SchedulerWorkSpace extends Widget<WorkspaceOptionsInternal> {
       endDayHour: 24,
       viewOffset: 0,
       hoursInterval: 0.5,
+      cellDuration: 30,
       activeStateEnabled: true,
       hoverStateEnabled: true,
       groups: [],

From bde4f6a5b8df3ca5d509eadfa7afbc2a9aa3f718 Mon Sep 17 00:00:00 2001
From: Sergei Burkatskii <noreply@github.com>
Date: Wed, 24 Jun 2026 13:11:25 +0200
Subject: [PATCH 13/17] fix: await appointment addition in tooltip test

---
 .../__internal/scheduler/__tests__/appointment_tooltip.test.ts  | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/devextreme/js/__internal/scheduler/__tests__/appointment_tooltip.test.ts b/packages/devextreme/js/__internal/scheduler/__tests__/appointment_tooltip.test.ts
index f4d646cd3a42..9d3de292ac14 100644
--- a/packages/devextreme/js/__internal/scheduler/__tests__/appointment_tooltip.test.ts
+++ b/packages/devextreme/js/__internal/scheduler/__tests__/appointment_tooltip.test.ts
@@ -438,7 +438,7 @@ describe.each([
 
         const initialTarget = POM.tooltip.target;
 
-        scheduler.addAppointment({
+        await scheduler.addAppointment({
           text: 'New Apt',
           startDate: new Date(2017, 4, 20, 9, 30),
           endDate: new Date(2017, 4, 20, 10, 30),

From d900cd8b9888d253efe2c010497ba48158047b7c Mon Sep 17 00:00:00 2001
From: Sergei Burkatskii <noreply@github.com>
Date: Wed, 24 Jun 2026 14:57:13 +0200
Subject: [PATCH 14/17] fix: fix tests related with deferred scrollto

---
 .../js/__internal/scheduler/m_scheduler.ts    | 39 +++++++++++--------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
index 5f4e75c0258e..ce46e174342c 100644
--- a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
+++ b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
@@ -935,11 +935,11 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     const result: DeferredObj<void> = Deferred();
 
     if (this._dataSource) {
-      this._dataSource.load().then(() => {
+      when(fromPromise(this._dataSource.load())).done(() => {
         hideLoading().catch(noop);
 
         this._fireContentReadyAction(result);
-      }).catch(() => {
+      }).fail(() => {
         hideLoading().catch(noop);
         result.reject();
       });
@@ -968,7 +968,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       result?.resolve();
     };
 
-    if (this.workSpaceRecalculation?.state() === 'pending') {
+    if (isDeferred(this.workSpaceRecalculation)) {
       this.workSpaceRecalculation.done(() => {
         fireContentReady();
       });
@@ -2113,11 +2113,14 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
     if (isPopupEditing) {
       this.appointmentPopup.show(singleRawAppointment, {
-        onSave: (newAppointment) => (
-          this.updateAppointment(rawAppointment, appointment.source)
-            .then(() => this.addAppointment(newAppointment as SafeAppointment))
-            .then(() => { this.scrollToAppointment(newAppointment as SafeAppointment); })
-        ),
+        onSave: (newAppointment) => {
+          const saveResult = when(
+            this.updateAppointment(rawAppointment, appointment.source)
+              .then(() => this.addAppointment(newAppointment as SafeAppointment)),
+          ).done(() => { this.scrollToAppointment(newAppointment as SafeAppointment); });
+
+          return saveResult.promise();
+        },
         title: messageLocalization.format('dxScheduler-editPopupTitle'),
         readOnly: Boolean(appointment.source) && appointment.disabled,
       });
@@ -2542,10 +2545,12 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       delete this.editAppointmentData; // TODO
       if (this.editing.allowAdding) {
         this.appointmentPopup.show(appointmentData, {
-          onSave: (appointment) => (
-            this.addAppointment(appointment as SafeAppointment)
-              .then(() => { this.scrollToAppointment(appointment as SafeAppointment); })
-          ),
+          onSave: (appointment) => {
+            const saveResult = when(this.addAppointment(appointment as SafeAppointment))
+              .done(() => { this.scrollToAppointment(appointment as SafeAppointment); });
+
+            return saveResult.promise();
+          },
           title: messageLocalization.format('dxScheduler-newPopupTitle'),
           readOnly: false,
         });
@@ -2570,10 +2575,12 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         const readOnly = isDisabled || !this.editing.allowUpdating;
 
         this.appointmentPopup.show(appointmentData, {
-          onSave: (appointment) => (
-            this.updateAppointment(appointmentData, appointment as SafeAppointment)
-              .then(() => { this.scrollToAppointment(appointment as SafeAppointment); })
-          ),
+          onSave: (appointment) => {
+            const saveResult = when(this.updateAppointment(appointmentData, appointment as SafeAppointment))
+              .done(() => { this.scrollToAppointment(appointment as SafeAppointment); });
+
+            return saveResult.promise();
+          },
           title: messageLocalization.format('dxScheduler-editPopupTitle'),
           readOnly,
         });

From 0eb95057f97c1035ff525c1d9f8b99b2cd869fcf Mon Sep 17 00:00:00 2001
From: Sergei Burkatskii <noreply@github.com>
Date: Wed, 24 Jun 2026 15:34:06 +0200
Subject: [PATCH 15/17] fix; try to fix tests

---
 .../js/__internal/scheduler/m_scheduler.ts    | 49 +++++++++++--------
 1 file changed, 28 insertions(+), 21 deletions(-)

diff --git a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
index ce46e174342c..69c74ec8c8db 100644
--- a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
+++ b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
@@ -935,10 +935,12 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     const result: DeferredObj<void> = Deferred();
 
     if (this._dataSource) {
-      when(fromPromise(this._dataSource.load())).done(() => {
+      // @ts-ignore
+      this._dataSource.load().done(() => {
         hideLoading().catch(noop);
 
         this._fireContentReadyAction(result);
+      // @ts-ignore
       }).fail(() => {
         hideLoading().catch(noop);
         result.reject();
@@ -968,8 +970,10 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       result?.resolve();
     };
 
-    if (isDeferred(this.workSpaceRecalculation)) {
-      this.workSpaceRecalculation.done(() => {
+    // @ts-ignore
+    // eslint-disable-next-line @typescript-eslint/no-misused-promises
+    if (this.workSpaceRecalculation) {
+      this.workSpaceRecalculation?.done(() => {
         fireContentReady();
       });
     } else {
@@ -2112,14 +2116,15 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
 
     if (isPopupEditing) {
+      // @ts-ignore
       this.appointmentPopup.show(singleRawAppointment, {
+        // @ts-ignore
         onSave: (newAppointment) => {
-          const saveResult = when(
-            this.updateAppointment(rawAppointment, appointment.source)
-              .then(() => this.addAppointment(newAppointment as SafeAppointment)),
-          ).done(() => { this.scrollToAppointment(newAppointment as SafeAppointment); });
-
-          return saveResult.promise();
+          // @ts-ignore
+          this.updateAppointment(rawAppointment, appointment.source);
+          // @ts-ignore
+          return when(this.addAppointment(newAppointment as SafeAppointment))
+            .done(() => { this.scrollToAppointment(newAppointment as SafeAppointment); });
         },
         title: messageLocalization.format('dxScheduler-editPopupTitle'),
         readOnly: Boolean(appointment.source) && appointment.disabled,
@@ -2544,13 +2549,14 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 
       delete this.editAppointmentData; // TODO
       if (this.editing.allowAdding) {
+        // @ts-ignore
         this.appointmentPopup.show(appointmentData, {
-          onSave: (appointment) => {
-            const saveResult = when(this.addAppointment(appointment as SafeAppointment))
-              .done(() => { this.scrollToAppointment(appointment as SafeAppointment); });
-
-            return saveResult.promise();
-          },
+          // @ts-ignore
+          onSave: (appointment) => (
+            // @ts-ignore
+            when(this.addAppointment(appointment as SafeAppointment))
+              .done(() => { this.scrollToAppointment(appointment as SafeAppointment); })
+          ),
           title: messageLocalization.format('dxScheduler-newPopupTitle'),
           readOnly: false,
         });
@@ -2574,13 +2580,14 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         const isDisabled = Boolean(adapter.source) && adapter.disabled;
         const readOnly = isDisabled || !this.editing.allowUpdating;
 
+        // @ts-ignore
         this.appointmentPopup.show(appointmentData, {
-          onSave: (appointment) => {
-            const saveResult = when(this.updateAppointment(appointmentData, appointment as SafeAppointment))
-              .done(() => { this.scrollToAppointment(appointment as SafeAppointment); });
-
-            return saveResult.promise();
-          },
+          // @ts-ignore
+          onSave: (appointment) => (
+            // @ts-ignore
+            when(this.updateAppointment(appointmentData, appointment as SafeAppointment))
+              .done(() => { this.scrollToAppointment(appointment as SafeAppointment); })
+          ),
           title: messageLocalization.format('dxScheduler-editPopupTitle'),
           readOnly,
         });

From 208022dd38bc0fa476e306e92cb57d78ed339980 Mon Sep 17 00:00:00 2001
From: Sergei Burkatskii <noreply@github.com>
Date: Wed, 24 Jun 2026 16:03:18 +0200
Subject: [PATCH 16/17] fix; try to fix tests

---
 .../js/__internal/scheduler/m_scheduler.ts    | 149 ++++++++----------
 1 file changed, 63 insertions(+), 86 deletions(-)

diff --git a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
index 69c74ec8c8db..904b86b2e523 100644
--- a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
+++ b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
@@ -2011,7 +2011,8 @@ class Scheduler extends SchedulerOptionsBaseWidget {
           this.updateAppointmentCore(
             appointmentData,
             newAppointmentData,
-          ).then(resolve);
+          // @ts-ignore
+          ).always(resolve);
         },
         false,
         undefined,
@@ -2022,15 +2023,16 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     });
   }
 
+  // @ts-ignore
   checkRecurringAppointment(
-    rawAppointment: SafeAppointment,
-    singleAppointment: SafeAppointment,
-    exceptionDate: Date,
-    callback: () => void,
-    isDeleted: boolean,
-    isPopupEditing?: boolean,
-    dragEvent?: SchedulerDragEvent | null,
-    recurrenceEditMode?: RecurrenceEditMode,
+    rawAppointment,
+    singleAppointment,
+    exceptionDate,
+    callback,
+    isDeleted,
+    isPopupEditing?,
+    dragEvent?,
+    recurrenceEditMode?,
     onCancel?: () => void,
   ): void {
     const recurrenceRule = this._dataAccessors.get('recurrenceRule', rawAppointment);
@@ -2051,7 +2053,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
           singleAppointment,
           exceptionDate,
           isDeleted,
-          Boolean(isPopupEditing),
+          isPopupEditing,
           dragEvent,
         );
         break;
@@ -2062,20 +2064,16 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         }
         this.showRecurrenceChangeConfirm(isDeleted)
           .done((editingMode) => {
-            if (editingMode === RECURRENCE_EDITING_MODE.SERIES) {
-              callback();
-            }
-
-            if (editingMode === RECURRENCE_EDITING_MODE.OCCURRENCE) {
-              this.excludeAppointmentFromSeries(
-                rawAppointment,
-                singleAppointment,
-                exceptionDate,
-                isDeleted,
-                Boolean(isPopupEditing),
-                dragEvent,
-              );
-            }
+            editingMode === RECURRENCE_EDITING_MODE.SERIES && callback();
+
+            editingMode === RECURRENCE_EDITING_MODE.OCCURRENCE && this.excludeAppointmentFromSeries(
+              rawAppointment,
+              singleAppointment,
+              exceptionDate,
+              isDeleted,
+              isPopupEditing,
+              dragEvent,
+            );
           })
           .fail(() => {
             if (this.option('_newAppointments')) {
@@ -2331,24 +2329,20 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this._workSpace.getDataByDroppableCell();
   }
 
-  updateAppointmentCore(
-    target: SafeAppointment,
-    rawAppointment: SafeAppointment,
-    onUpdatePrevented?: () => void,
-    dragEvent?: SchedulerDragEvent | null,
-  ): Promise<void> {
+  // @ts-ignore
+  updateAppointmentCore(target, rawAppointment, onUpdatePrevented?, dragEvent?) {
     const updatingOptions = {
       newData: rawAppointment,
       oldData: extend({}, target),
       cancel: false,
     };
 
-    const performFailAction = function performFailAction(this: Scheduler, err?: Error): void {
+    const performFailAction = function (err?) {
       if (onUpdatePrevented) {
         onUpdatePrevented.call(this);
       }
 
-      if (err?.name === 'Error') {
+      if (err && err.name === 'Error') {
         throw err;
       }
     }.bind(this);
@@ -2356,41 +2350,44 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.actions[StoreEventNames.UPDATING](updatingOptions);
 
     if (dragEvent && !isDeferred(dragEvent.cancel)) {
-      dragEvent.cancel = Deferred<boolean>();
+      // @ts-expect-error
+      dragEvent.cancel = new Deferred();
     }
 
     if (isPromise(updatingOptions.cancel) && (dragEvent || this.option('_newAppointments'))) {
       this.updatingAppointments.add(target);
     }
 
-    return this.processActionResult(updatingOptions, (canceled) => {
+    return this.processActionResult(updatingOptions, function (canceled) {
+      // @ts-expect-error
+      let deferred = new Deferred();
+
       if (!canceled) {
         this.expandAllDayPanel(rawAppointment);
 
         try {
-          return this.appointmentDataSource
+          deferred = this.appointmentDataSource
             .update(target, rawAppointment)
             .done(() => {
               dragEvent?.cancel.resolve(false);
             })
             .always((storeAppointment) => {
               this.updatingAppointments.delete(target);
-              if (isDefined(storeAppointment)) {
-                this.onDataPromiseCompleted(StoreEventNames.UPDATED, storeAppointment);
-              }
+              this.onDataPromiseCompleted(StoreEventNames.UPDATED, storeAppointment);
             })
-            .fail(() => performFailAction())
-            .then(() => undefined);
-        } catch (err: unknown) {
-          performFailAction(err instanceof Error ? err : undefined);
+            .fail(() => performFailAction());
+        } catch (err) {
+          performFailAction(err);
           this.updatingAppointments.delete(target);
-          return Deferred().resolve().promise();
+          deferred.resolve();
         }
+      } else {
+        performFailAction();
+        this.updatingAppointments.delete(target);
+        deferred.resolve();
       }
 
-      performFailAction();
-      this.updatingAppointments.delete(target);
-      return Deferred().resolve().promise();
+      return deferred.promise();
     });
   }
 
@@ -2527,67 +2524,47 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.showAppointmentPopup(resultAppointment, true);
   }
 
-  showAppointmentPopup(
-    rawAppointment?: SafeAppointment,
-    createNewAppointment?: boolean,
-    rawTargetedAppointment?: SafeAppointment | TargetedAppointment,
-  ): void {
-    const newRawTargetedAppointment = rawTargetedAppointment
-      ? { ...rawTargetedAppointment }
-      : {} as SafeAppointment;
-    if (rawTargetedAppointment) {
+  // @ts-ignore
+  showAppointmentPopup(rawAppointment?, createNewAppointment?, rawTargetedAppointment?) {
+    const newRawTargetedAppointment = { ...rawTargetedAppointment };
+    if (newRawTargetedAppointment) {
       delete newRawTargetedAppointment.displayStartDate;
       delete newRawTargetedAppointment.displayEndDate;
     }
 
+    const newTargetedAppointment = extend({}, rawAppointment, newRawTargetedAppointment);
+
     const isCreateAppointment = createNewAppointment ?? isEmptyObject(rawAppointment);
 
-    if (isCreateAppointment) {
-      const appointmentData = isEmptyObject(rawAppointment)
-        ? this.createPopupAppointment()
-        : rawAppointment as SafeAppointment;
+    if (isEmptyObject(rawAppointment)) {
+      rawAppointment = this.createPopupAppointment();
+    }
 
+    if (isCreateAppointment) {
       delete this.editAppointmentData; // TODO
       if (this.editing.allowAdding) {
-        // @ts-ignore
-        this.appointmentPopup.show(appointmentData, {
+        this.appointmentPopup.show(rawAppointment, {
           // @ts-ignore
-          onSave: (appointment) => (
-            // @ts-ignore
-            when(this.addAppointment(appointment as SafeAppointment))
-              .done(() => { this.scrollToAppointment(appointment as SafeAppointment); })
-          ),
+          onSave: (appointment) => when(this.addAppointment(appointment))
+            .done(() => { this.scrollToAppointment(appointment); }),
           title: messageLocalization.format('dxScheduler-newPopupTitle'),
           readOnly: false,
         });
       }
     } else {
-      const appointmentData = rawAppointment as SafeAppointment;
-      const newTargetedAppointment = extend(
-        {},
-        appointmentData,
-        newRawTargetedAppointment,
-      ) as SafeAppointment;
-      const startDate = this._dataAccessors.get(
-        'startDate',
-        Object.keys(newRawTargetedAppointment).length ? newRawTargetedAppointment : appointmentData,
-      );
+      const startDate = this._dataAccessors.get('startDate', newRawTargetedAppointment || rawAppointment);
 
-      this.checkRecurringAppointment(appointmentData, newTargetedAppointment, startDate, () => {
-        this.editAppointmentData = appointmentData; // TODO
+      this.checkRecurringAppointment(rawAppointment, newTargetedAppointment, startDate, () => {
+        this.editAppointmentData = rawAppointment; // TODO
 
-        const adapter = new AppointmentAdapter(appointmentData, this._dataAccessors);
+        const adapter = new AppointmentAdapter(rawAppointment, this._dataAccessors);
         const isDisabled = Boolean(adapter.source) && adapter.disabled;
         const readOnly = isDisabled || !this.editing.allowUpdating;
 
-        // @ts-ignore
-        this.appointmentPopup.show(appointmentData, {
+        this.appointmentPopup.show(rawAppointment, {
           // @ts-ignore
-          onSave: (appointment) => (
-            // @ts-ignore
-            when(this.updateAppointment(appointmentData, appointment as SafeAppointment))
-              .done(() => { this.scrollToAppointment(appointment as SafeAppointment); })
-          ),
+          onSave: (appointment) => when(this.updateAppointment(rawAppointment, appointment))
+            .done(() => { this.scrollToAppointment(appointment); }),
           title: messageLocalization.format('dxScheduler-editPopupTitle'),
           readOnly,
         });

From 1d1aab6babcd2b2c5f191c2077ab48359a153e62 Mon Sep 17 00:00:00 2001
From: Sergei Burkatskii <noreply@github.com>
Date: Wed, 24 Jun 2026 16:39:53 +0200
Subject: [PATCH 17/17] refactor: refactor after fixes

---
 .../js/__internal/scheduler/m_scheduler.ts    | 165 ++++++++++--------
 1 file changed, 95 insertions(+), 70 deletions(-)

diff --git a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
index 904b86b2e523..a6e6000861e2 100644
--- a/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
+++ b/packages/devextreme/js/__internal/scheduler/m_scheduler.ts
@@ -935,12 +935,10 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     const result: DeferredObj<void> = Deferred();
 
     if (this._dataSource) {
-      // @ts-ignore
-      this._dataSource.load().done(() => {
+      when(fromPromise(this._dataSource.load())).done(() => {
         hideLoading().catch(noop);
 
         this._fireContentReadyAction(result);
-      // @ts-ignore
       }).fail(() => {
         hideLoading().catch(noop);
         result.reject();
@@ -970,10 +968,8 @@ class Scheduler extends SchedulerOptionsBaseWidget {
       result?.resolve();
     };
 
-    // @ts-ignore
-    // eslint-disable-next-line @typescript-eslint/no-misused-promises
-    if (this.workSpaceRecalculation) {
-      this.workSpaceRecalculation?.done(() => {
+    if (isDeferred(this.workSpaceRecalculation)) {
+      this.workSpaceRecalculation.done(() => {
         fireContentReady();
       });
     } else {
@@ -1520,6 +1516,15 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this._workSpace.updateScrollPosition(startDate, appointmentGroupValues, inAllDayRow);
   }
 
+  private saveAppointmentAndScroll(
+    saveAction: () => PromiseLike<void>,
+    appointment: SafeAppointment,
+  ): PromiseLike<void> {
+    return when(saveAction()).done(() => {
+      this.scrollToAppointment(appointment);
+    }).promise();
+  }
+
   private getAppointmentTooltipOptions(): AppointmentTooltipOptions {
     return {
       createComponent: this._createComponent.bind(this) as AppointmentTooltipOptions['createComponent'],
@@ -2008,11 +2013,10 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         newAppointmentData,
         startDate,
         () => {
-          this.updateAppointmentCore(
+          when(fromPromise(this.updateAppointmentCore(
             appointmentData,
             newAppointmentData,
-          // @ts-ignore
-          ).always(resolve);
+          ))).always(resolve);
         },
         false,
         undefined,
@@ -2023,16 +2027,15 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     });
   }
 
-  // @ts-ignore
   checkRecurringAppointment(
-    rawAppointment,
-    singleAppointment,
-    exceptionDate,
-    callback,
-    isDeleted,
-    isPopupEditing?,
-    dragEvent?,
-    recurrenceEditMode?,
+    rawAppointment: SafeAppointment,
+    singleAppointment: SafeAppointment,
+    exceptionDate: Date,
+    callback: () => void,
+    isDeleted: boolean,
+    isPopupEditing?: boolean,
+    dragEvent?: SchedulerDragEvent | null,
+    recurrenceEditMode?: RecurrenceEditMode,
     onCancel?: () => void,
   ): void {
     const recurrenceRule = this._dataAccessors.get('recurrenceRule', rawAppointment);
@@ -2053,7 +2056,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
           singleAppointment,
           exceptionDate,
           isDeleted,
-          isPopupEditing,
+          Boolean(isPopupEditing),
           dragEvent,
         );
         break;
@@ -2064,16 +2067,20 @@ class Scheduler extends SchedulerOptionsBaseWidget {
         }
         this.showRecurrenceChangeConfirm(isDeleted)
           .done((editingMode) => {
-            editingMode === RECURRENCE_EDITING_MODE.SERIES && callback();
-
-            editingMode === RECURRENCE_EDITING_MODE.OCCURRENCE && this.excludeAppointmentFromSeries(
-              rawAppointment,
-              singleAppointment,
-              exceptionDate,
-              isDeleted,
-              isPopupEditing,
-              dragEvent,
-            );
+            if (editingMode === RECURRENCE_EDITING_MODE.SERIES) {
+              callback();
+            }
+
+            if (editingMode === RECURRENCE_EDITING_MODE.OCCURRENCE) {
+              this.excludeAppointmentFromSeries(
+                rawAppointment,
+                singleAppointment,
+                exceptionDate,
+                isDeleted,
+                Boolean(isPopupEditing),
+                dragEvent,
+              );
+            }
           })
           .fail(() => {
             if (this.option('_newAppointments')) {
@@ -2114,15 +2121,13 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     }
 
     if (isPopupEditing) {
-      // @ts-ignore
       this.appointmentPopup.show(singleRawAppointment, {
-        // @ts-ignore
         onSave: (newAppointment) => {
-          // @ts-ignore
-          this.updateAppointment(rawAppointment, appointment.source);
-          // @ts-ignore
-          return when(this.addAppointment(newAppointment as SafeAppointment))
-            .done(() => { this.scrollToAppointment(newAppointment as SafeAppointment); });
+          this.updateAppointment(rawAppointment, appointment.source).catch(noop);
+          return this.saveAppointmentAndScroll(
+            () => this.addAppointment(newAppointment as SafeAppointment),
+            newAppointment as SafeAppointment,
+          );
         },
         title: messageLocalization.format('dxScheduler-editPopupTitle'),
         readOnly: Boolean(appointment.source) && appointment.disabled,
@@ -2329,20 +2334,24 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     return this._workSpace.getDataByDroppableCell();
   }
 
-  // @ts-ignore
-  updateAppointmentCore(target, rawAppointment, onUpdatePrevented?, dragEvent?) {
+  updateAppointmentCore(
+    target: SafeAppointment,
+    rawAppointment: SafeAppointment,
+    onUpdatePrevented?: () => void,
+    dragEvent?: SchedulerDragEvent | null,
+  ): Promise<void> {
     const updatingOptions = {
       newData: rawAppointment,
       oldData: extend({}, target),
       cancel: false,
     };
 
-    const performFailAction = function (err?) {
+    const performFailAction = function performFailAction(this: Scheduler, err?: Error): void {
       if (onUpdatePrevented) {
         onUpdatePrevented.call(this);
       }
 
-      if (err && err.name === 'Error') {
+      if (err?.name === 'Error') {
         throw err;
       }
     }.bind(this);
@@ -2350,17 +2359,15 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.actions[StoreEventNames.UPDATING](updatingOptions);
 
     if (dragEvent && !isDeferred(dragEvent.cancel)) {
-      // @ts-expect-error
-      dragEvent.cancel = new Deferred();
+      dragEvent.cancel = Deferred<boolean>();
     }
 
     if (isPromise(updatingOptions.cancel) && (dragEvent || this.option('_newAppointments'))) {
       this.updatingAppointments.add(target);
     }
 
-    return this.processActionResult(updatingOptions, function (canceled) {
-      // @ts-expect-error
-      let deferred = new Deferred();
+    return this.processActionResult(updatingOptions, function onUpdate(this: Scheduler, canceled) {
+      let deferred: DeferredObj<unknown> = Deferred();
 
       if (!canceled) {
         this.expandAllDayPanel(rawAppointment);
@@ -2369,15 +2376,18 @@ class Scheduler extends SchedulerOptionsBaseWidget {
           deferred = this.appointmentDataSource
             .update(target, rawAppointment)
             .done(() => {
-              dragEvent?.cancel.resolve(false);
+              dragEvent?.cancel?.resolve(false);
             })
             .always((storeAppointment) => {
               this.updatingAppointments.delete(target);
-              this.onDataPromiseCompleted(StoreEventNames.UPDATED, storeAppointment);
+              this.onDataPromiseCompleted(
+                StoreEventNames.UPDATED,
+                storeAppointment as SafeAppointment,
+              );
             })
             .fail(() => performFailAction());
-        } catch (err) {
-          performFailAction(err);
+        } catch (err: unknown) {
+          performFailAction(err instanceof Error ? err : undefined);
           this.updatingAppointments.delete(target);
           deferred.resolve();
         }
@@ -2524,47 +2534,62 @@ class Scheduler extends SchedulerOptionsBaseWidget {
     this.showAppointmentPopup(resultAppointment, true);
   }
 
-  // @ts-ignore
-  showAppointmentPopup(rawAppointment?, createNewAppointment?, rawTargetedAppointment?) {
-    const newRawTargetedAppointment = { ...rawTargetedAppointment };
-    if (newRawTargetedAppointment) {
+  showAppointmentPopup(
+    rawAppointment?: SafeAppointment,
+    createNewAppointment?: boolean,
+    rawTargetedAppointment?: SafeAppointment | TargetedAppointment,
+  ): void {
+    const newRawTargetedAppointment: SafeAppointment = rawTargetedAppointment
+      ? { ...rawTargetedAppointment }
+      : {} as SafeAppointment;
+    if (rawTargetedAppointment) {
       delete newRawTargetedAppointment.displayStartDate;
       delete newRawTargetedAppointment.displayEndDate;
     }
 
-    const newTargetedAppointment = extend({}, rawAppointment, newRawTargetedAppointment);
+    const newTargetedAppointment = extend(
+      {},
+      rawAppointment,
+      newRawTargetedAppointment,
+    ) as SafeAppointment;
 
     const isCreateAppointment = createNewAppointment ?? isEmptyObject(rawAppointment);
 
-    if (isEmptyObject(rawAppointment)) {
-      rawAppointment = this.createPopupAppointment();
+    let appointment: SafeAppointment = rawAppointment ?? {} as SafeAppointment;
+    if (isEmptyObject(appointment)) {
+      appointment = this.createPopupAppointment();
     }
 
     if (isCreateAppointment) {
       delete this.editAppointmentData; // TODO
       if (this.editing.allowAdding) {
-        this.appointmentPopup.show(rawAppointment, {
-          // @ts-ignore
-          onSave: (appointment) => when(this.addAppointment(appointment))
-            .done(() => { this.scrollToAppointment(appointment); }),
+        this.appointmentPopup.show(appointment, {
+          onSave: (appointmentData) => this.saveAppointmentAndScroll(
+            () => this.addAppointment(appointmentData as SafeAppointment),
+            appointmentData as SafeAppointment,
+          ),
           title: messageLocalization.format('dxScheduler-newPopupTitle'),
           readOnly: false,
         });
       }
     } else {
-      const startDate = this._dataAccessors.get('startDate', newRawTargetedAppointment || rawAppointment);
+      const startDate = this._dataAccessors.get(
+        'startDate',
+        Object.keys(newRawTargetedAppointment).length ? newRawTargetedAppointment : appointment,
+      );
 
-      this.checkRecurringAppointment(rawAppointment, newTargetedAppointment, startDate, () => {
-        this.editAppointmentData = rawAppointment; // TODO
+      this.checkRecurringAppointment(appointment, newTargetedAppointment, startDate, () => {
+        this.editAppointmentData = appointment; // TODO
 
-        const adapter = new AppointmentAdapter(rawAppointment, this._dataAccessors);
+        const adapter = new AppointmentAdapter(appointment, this._dataAccessors);
         const isDisabled = Boolean(adapter.source) && adapter.disabled;
         const readOnly = isDisabled || !this.editing.allowUpdating;
 
-        this.appointmentPopup.show(rawAppointment, {
-          // @ts-ignore
-          onSave: (appointment) => when(this.updateAppointment(rawAppointment, appointment))
-            .done(() => { this.scrollToAppointment(appointment); }),
+        this.appointmentPopup.show(appointment, {
+          onSave: (appointmentData) => this.saveAppointmentAndScroll(
+            () => this.updateAppointment(appointment, appointmentData as SafeAppointment),
+            appointmentData as SafeAppointment,
+          ),
           title: messageLocalization.format('dxScheduler-editPopupTitle'),
           readOnly,
         });
@@ -2862,7 +2887,7 @@ class Scheduler extends SchedulerOptionsBaseWidget {
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
 (Scheduler as any).include(DataHelperMixin);
 
-// @ts-ignore
+// @ts-expect-error DataHelperMixin changes Scheduler prototype
 registerComponent('dxScheduler', Scheduler);
 
 export default Scheduler;