fix(datetime-button): time-only values are parsed (#26852)

resolves #26851

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

@@ -168,4 +168,13 @@ describe('getLocalizedTime', () => {
 
     expect(getLocalizedTime('en-GB', datetimeParts, false)).toEqual('12:00 am');
   });
+  it('should parse time-only values correctly', () => {
+    const datetimeParts = {
+      hour: 22,
+      minute: 40,
+    };
+
+    expect(getLocalizedTime('en-US', datetimeParts, false)).toEqual('10:40 PM');
+    expect(getLocalizedTime('en-US', datetimeParts, true)).toEqual('22:40');
+  });
 });

core/src/components/datetime/utils/format.ts

@@ -11,7 +11,12 @@ const getFormattedDayPeriod = (dayPeriod?: string) => {
 };
 
 export const getLocalizedTime = (locale: string, refParts: DatetimeParts, use24Hour: boolean): string => {
-  if (refParts.hour === undefined || refParts.minute === undefined) {
+  const timeParts: Pick<DatetimeParts, 'hour' | 'minute'> = {
+    hour: refParts.hour,
+    minute: refParts.minute,
+  };
+
+  if (timeParts.hour === undefined || timeParts.minute === undefined) {
     return 'Invalid Time';
   }
 
@@ -27,7 +32,21 @@ export const getLocalizedTime = (locale: string, refParts: DatetimeParts, use24H
   }).format(
     new Date(
       convertDataToISO({
-        ...refParts,
+        /**
+         * JS uses a simplified ISO 8601 format which allows for
+         * date-only formats and date-time formats, but not
+         * time-only formats: https://tc39.es/ecma262/#sec-date-time-string-format
+         * As a result, developers who only pass a time will get
+         * an "Invalid Date" error. To account for this, we make sure that
+         * year/day/month values are set when passing to new Date().
+         * The Intl.DateTimeFormat call above only uses the hour/minute
+         * values, so passing these date values should have no impact
+         * on the time output.
+         */
+        year: 2023,
+        day: 1,
+        month: 1,
+        ...timeParts,
         // TODO: FW-1831 will remove the need to manually set the tzOffset to undefined
         tzOffset: undefined,
       })