Is there any possible way to find the timezone using the ISOtime format in javascript

Question

localDate: "2020-10-13" localTime: "20:00:00" dateTime: "2020-10-14T01:00:00Z"

I have these three datas, how to find the timezone using these data.

Short answer: you can't. You can guess. That's the best you can do. — Mike 'Pomax' Kamermans, Feb 12 '20 at 01:24
Does this answer your question? [How to ISO 8601 format a Date with Timezone Offset in JavaScript?](https://stackoverflow.com/questions/17415579/how-to-iso-8601-format-a-date-with-timezone-offset-in-javascript) — keikai, Feb 12 '20 at 01:26
If you can you get it in real time, then yes. If you mean retroactively, like if you're just given a random time string then there's nothing in a timestamp like that which tells you what timezone it's from — Jayce444, Feb 12 '20 at 01:27
Based on hour difference we cannot able to find the timezone? — user8171294, Feb 12 '20 at 01:30
Is your question how to get the time zone from only those three facts, or how to determine the user’s time zone from the browser? The latter is easy; the former is more challenging. — Heretic Monkey, Feb 12 '20 at 01:30
By literally guessing. "8pm on the 13th" is the same as "1 am on the 14th but offset by 4 hours", so it's _probably_ UTC-4, but most certainly not _without question_ UTC-4. — Mike 'Pomax' Kamermans, Feb 12 '20 at 01:31
Then you’ll need a lookup table of all of the time zones and the dates and times they changed, for at least the geographical, political, and temporal regions you are interested in. Good luck! — Heretic Monkey, Feb 12 '20 at 01:39
Of course I do, but given who asked this question, it's disappointing to see you pointing that out rather than user 8171294. — Mike 'Pomax' Kamermans, Feb 12 '20 at 23:40

score 0 · Answer 1 · answered Feb 12 '20 at 23:48

Assuming your inputs are exactly as given:

var localDate = "2020-10-13";
var localTime = "20:00:00";
var dateTime = "2020-10-14T01:00:00Z";

var offsetMillis = new Date(localDate + 'T' + localTime + 'Z') - new Date(dateTime);
var offsetHours = offsetMillis / 36e5;
console.log(offsetHours); // -5

The result is -5, which is 5 hours behind UTC. This works by creating two date objects, one that is UTC-based, and one that pretends to be UTC-based but is actually using the local values. Subtracting the two yields the offset.

Keep in mind - this is an offset from UTC, not a time zone. One cannot determine the time zone from the offset alone. See "Time Zone != Offset" in the timezone tag wiki for more details.

Also keep in mind that not all time zone offsets will be in whole hours. For example, India uses UTC-5:30, so expect -5.5 from this code in such a case. (There also exist time zones with 45-minute offsets.)

Is there any possible way to find the timezone using the ISOtime format in javascript

1 Answers1