fix(datetime): date strings no longer revert to previous day (#18018)

fixes #17977

core/src/components/datetime/datetime-util.ts

@@ -248,8 +248,20 @@ export function parseDate(val: string | undefined | null): DatetimeData | undefi
  * such as "01:47"
  */
 export const getLocalDateTime = (dateString: any = ''): Date => {
-  const date = (typeof dateString === 'string' && dateString.length > 0) ? new Date(dateString) : new Date();
+  /**
+   * Ensures that YYYY-MM-DD, YYYY-MM,
+   * YYYY-DD, etc does not get affected
+   * by timezones and stays on the day/month
+   * that the user provided
+   */
+  if (
+    dateString.length === 10 ||
+    dateString.length === 7
+  ) {
+    dateString += ' ';
+  }
 
+  const date = (typeof dateString === 'string' && dateString.length > 0) ? new Date(dateString) : new Date();
   return new Date(
     Date.UTC(
       date.getFullYear(),
@@ -267,7 +279,6 @@ export function updateDate(existingData: DatetimeData, newData: any): boolean {
 
   if (!newData || typeof newData === 'string') {
     const localDateTime = getLocalDateTime(newData);
-
     if (!Number.isNaN(localDateTime.getTime())) {
       newData = localDateTime.toISOString();
     }

core/src/components/datetime/test/datetime.spec.ts

@@ -52,6 +52,23 @@ describe('Datetime', () => {
         expect(convertToLocal.toISOString()).toEqual(expectedDateString);
       });
     });
+    
+    it('should format a date string and not get affected by the timezone offset', () => {
+
+      const dateStringTests = [
+        { input: '2019-03-20', expectedOutput: '2019-03-20' },
+        { input: '1994-04-15', expectedOutput: '1994-04-15' },
+        { input: '2008-09-02', expectedOutput: '2008-09-02' },
+        { input: '1995-02', expectedOutput: '1995-02' },
+        { input: '1994-03-14', expectedOutput: '1994-03-14' },
+        { input: '9 01:47', expectedOutput: '09-01T01:47' }
+      ];
+
+      dateStringTests.forEach(test => {
+        const convertToLocal = getLocalDateTime(test.input);
+        expect(convertToLocal.toISOString()).toContain(test.expectedOutput);
+      });
+    });
   });
 
   describe('daysInMonth()', () => {