Force date to a given time zone

August 14, 2021

2 min read

#Why do I need this?

I set the dates for my blog posts in YYYY-MM-DD format, like this 2021-07-09 for July 9th, 2021. I use a package called gray-matter to parse this date out of the frontmatter of my blog posts. Because I omit any timezone information in my dates, they get parsed as UTC-0:00. This makes sense as a software default, but I'm authoring from PST not GMT! If you have a similar scenario, you might find this function useful too.

#Code

/**
 * This function will discard the time component of the provided
 * date and then convert it to the provided time zone. This can be used to
 * persist the year/month/day components of a Date in a new time zone.
 *
 *
 * ex.
 * Without this function:
 * new Date('2021-07-09T00:00:00.000Z') would convert to
 * Thu Jul 08 2021 17:00:00 GMT-0700 (Pacific Daylight Time).
 *
 * Note that we've ended with a July 8th date, instead of the 9th.
 *
 *
 * With this function:
 * forceDateToTimeZone(new Date('2021-07-09T00:00:00.000Z'), 'PST') you get
 * Fri Jul 09 2021 01:00:00 GMT-0700 (Pacific Daylight Time).
 *
 * Note that both dates read July 9th now.
 */
const forceDateToTimeZone = (date, timeZone) => {
  const [isoDate, isoTime] = date.toISOString().split("T");

  return new Date(`${isoDate} ${timeZone}`);
};