Converting Central Time date to ISO string in current timezone

Question

I have a date I know is stored in Central Time. It has the following format: 2017-11-19T23:39:35.280000. I want to turn this into an ISO-formatted date in the current timezone. I got it to work when simply creating a new Date() -- but then when I subsequently call .toISOString(), it goes haywire. Here's the code:

function convertCentralToLocal() {
  const centralOffset = 360;
  const dateInCentralMs = new Date('2017-11-19T23:39:35.280000').getTime();
  const now = new Date();
  const localOffset = now.getTimezoneOffset();

  // this works: Sun Nov 19 2017 23:39:35 GMT-0600 (CST)
  const d = new Date(dateInCentralMs + ((centralOffset - localOffset) * 60000));

  // this seems to give the date six hours off: 2017-11-20T05:39:35.280Z
  const iso = d.toISOString();
}

Is it an issue with GMT? I'm feeling lost.

"CST" I guess is US Central Standard Time, not Cuba Standard Time or China Standard Time. The US CST is UTC -0600. Don't use the built-in parser, see [*Why does Date.parse give incorrect results?*](https://stackoverflow.com/questions/2587345/why-does-date-parse-give-incorrect-results) The *toISOString* method is always UTC, both strings represent the same moment in time but in different timezones. Also see [*Where can I find documentation on formatting a date in JavaScript?*](https://stackoverflow.com/questions/1056728/where-can-i-find-documentation-on-formatting-a-date-in-javascript) — RobG, Nov 21 '17 at 10:40

Gabriel Heming · Answer 1 · 2017-11-20T17:39:09.363

It's true that ISO 8601 doesn't define a fixed timezone to represent the Date/Time, but it does define symbols to represent the timezone and a few date/time formats as well:

Date and Time Formats

TZD = time zone designator (Z or +hh:mm or -hh:mm)

Date.prototype.toISOString()

At MDN you can read that the timezone will be always zero UTC offset:

The toISOString() method returns a string in simplified extended ISO format (ISO 8601), which is always 24 or 27 characters long (YYYY-MM-DDTHH:mm:ss.sssZ or ±YYYYYY-MM-DDTHH:mm:ss.sssZ, respectively). The timezone is always zero UTC offset, as denoted by the suffix "Z".

It's a particularity from Date.toISOStringMethod. On the same way that a fixed format was chosen (YYYY-MM-DDTHH:mm:ss.sssZ or ±YYYYYY-MM-DDTHH:mm:ss.sssZ), it had been chosen a specific timezone to ISO representation.

To workaround this particularity, you could implement the method toISOString() as shown in this link below or just use your own example.

Converting Central Time date to ISO string in current timezone

1 Answers1