fix: Selecting dates between DST and non DST timezone results in hours updating every selection (fixes #991)

Author: Jasenkoo

src/VueDatePicker/composables/external-internal-mapper.ts

@@ -63,7 +63,7 @@ export const useExternalInternalMapper = (emit: VueEmit, props: AllPropsType, is
 
     const convertZonedModelToLocal = (date: Date) => {
         if (defaultedTz.value.timezone && defaultedTz.value.convertModel) {
-            const offset = getTimezoneOffset(defaultedTz.value.timezone);
+            const offset = getTimezoneOffset(defaultedTz.value.timezone, date);
             return addHours(date, offset);
         }
         return date;
@@ -394,7 +394,6 @@ export const useExternalInternalMapper = (emit: VueEmit, props: AllPropsType, is
         return getWeekFromDate(internalModelValue.value, props.weekStart).map((date) => getDate(date));
     };
 
-     
     const modeEmitter = (mapper: any, returnOnly: boolean) =>
         emitValue(convertType(mapInternalToSpecificExternal(mapper)), false, returnOnly);
 

src/VueDatePicker/utils/defaults.ts

@@ -88,7 +88,7 @@ export const defaultMultiCalendars = (multiCalendars?: MultiCalendarsProp): Mult
     };
     if (!multiCalendars) return { ...defaultOptions, count: getMultiCalendarsCount(false) };
     const addOptions = isConfig ? multiCalendars : ({} as MultiCalendarsOptions);
-    const option = isConfig ? addOptions.count ?? true : multiCalendars;
+    const option = isConfig ? (addOptions.count ?? true) : multiCalendars;
     const count = getMultiCalendarsCount(option);
 
     return Object.assign(defaultOptions, addOptions, { count });

src/VueDatePicker/utils/timezone.ts

@@ -28,11 +28,11 @@ export const sanitizeDateToLocal = (date: MaybeDate, tz?: TimeZoneConfig, reset?
     return tz.exactMatch ? getDateInTz(date, tz, reset) : localToTz(newDate, tz.timezone);
 };
 
-export const getTimezoneOffset = (timezone?: string) => {
+export const getTimezoneOffset = (timezone?: string, localDate?: Date) => {
     if (!timezone) return 0;
     const date = new Date();
     const utcDate = new Date(date.toLocaleString('en-US', { timeZone: 'UTC' }));
     const specificDate = new Date(date.toLocaleString('en-US', { timeZone: timezone }));
-    const dstOffset = specificDate.getTimezoneOffset() / 60;
+    const dstOffset = (localDate ?? specificDate).getTimezoneOffset() / 60;
     return (+utcDate - +specificDate) / (1000 * 60 * 60) - dstOffset;
 };