RSSHub/lib/utils/parse-date-in-timezone.ts

import dayjs from 'dayjs';
import utc from 'dayjs/plugin/utc.js';

dayjs.extend(utc);

const isWallClockCandidate = (date: string | number | Date): date is string => typeof date === 'string';

// Interpret a source's wall clock without using the host's timezone. Dates,
// timestamps and ISO strings with an explicit offset already identify an instant.
export const parseDateInTimezone = (date: string | number | Date, offset: number): Date => {
    const parsed = dayjs.utc(date);
    if (!isWallClockCandidate(date) || /(?:Z|[+-]\d{2}:?\d{2}|(?:GMT|UTC)(?:[+-]\d{1,4})?)$/i.test(date.trim())) {
        return parsed.toDate();
    }
    return parsed.subtract(offset, 'hour').toDate();
};