DateBox: Preserve selected date part after focusout + focusin (T1318439)

packages/devextreme/js/__internal/ui/date_box/m_date_box.mask.ts

@@ -11,6 +11,7 @@ import { fitIntoRange, inRange, sign } from '@js/core/utils/math';
 import {
   isDate, isDefined, isFunction, isString,
 } from '@js/core/utils/type';
+import type { DxEvent } from '@js/events';
 import type { Properties } from '@js/ui/date_box';
 import dateLocalization from '@ts/core/localization/date';
 
@@ -661,18 +662,22 @@ class DateBoxMask extends DateBoxBase {
     }
   }
 
-  _enterHandler() {
+  _enterHandler(): void {
     this._fireChangeEvent();
-    this._selectNextPart(FORWARD);
+
+    if (this._useMaskBehavior() && this._isAllSelected()) {
+      this._selectFirstPart();
+    } else {
+      this._selectNextPart(FORWARD);
+    }
   }
 
-  _focusOutHandler(e) {
+  _focusOutHandler(e: DxEvent): void {
     const shouldFireChangeEvent = this._useMaskBehavior() && !e.isDefaultPrevented();
 
     if (shouldFireChangeEvent) {
       this._fireChangeEvent();
       super._focusOutHandler(e);
-      this._selectFirstPart();
     } else {
       super._focusOutHandler(e);
     }

packages/devextreme/testing/tests/DevExpress.ui.widgets.editors/datebox.mask.tests.js

@@ -1866,6 +1866,24 @@ module('Caret moving', setupModule, () => {
 
         assert.deepEqual(this.keyboard.caret(), allSelectedCaret, 'no date part is selected');
     });
+
+    test('should keep active part after focus out and focus in (T1318439)', function(assert) {
+        const caretYear = { start: 11, end: 15 };
+
+        this.instance.option({
+            useMaskBehavior: true,
+            mode: 'text',
+        });
+
+        this.keyboard.press('end');
+
+        assert.deepEqual(this.keyboard.caret(), caretYear, 'year is selected initially');
+
+        this.$input.trigger('focusout');
+        this.$input.trigger('focusin');
+
+        assert.deepEqual(this.keyboard.caret(), caretYear, 'year is selected after focus return');
+    });
 });
 
 module('Using beforeInput event', {