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I want to convert the UTC ISO 8601 date string into the user's local date time based on the user's Time Zone. I'm using moment-timezone to accomplish this task, and here is the code snippet:

const userTimezone = moment.tz.guess();
const time = moment.utc("2023-03-08T16:35:21.453")
                   .tz(userTimezone)
                   .format("MM/DD/YYYY h:mm A")

Does Moment Timezone consider the DST rules of the selected time zone and apply the appropriate DST offset to the formatted time?

If my date string falls under DST then will it automatically adjust for DST offset while formatting or do we have to adjust for DST Offset manually?

Peter Mortensen
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programmers_view
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  • If you try say "2023-01-01T00" and "2023-07-01T00" with a location that observes DST you'll likely find out in less time that it took you to ask the question. ;-) The answer is "yes". – RobG Jun 16 '23 at 10:48
  • @Yogi—it's not deprecated, it's described as "done", i.e. no new features, serious bug fixes only. I think the OP's real issue is parsing the timestamp as UTC (which could be done by appending a Z and using *Date.parse*). – RobG Jun 16 '23 at 10:51
  • @RobG Thanks for the info man, really appreciated it! – programmers_view Jun 16 '23 at 12:20

1 Answers1

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Moment Timezone does consider the DST (Daylight Saving Time) rules of the selected time zone and applies the appropriate DST offset to the formatted time. When you use the tz() function with Moment Timezone, it takes into account the time zone's DST rules and adjusts the time accordingly.

In your code snippet, when you call moment.utc("2023-03-08T16:35:21.453"), you are specifying a UTC time. Then, by chaining .tz(userTimezone), you are converting that UTC time to the user's local time based on their time zone, including any DST adjustments if applicable.

Therefore, when you format the time using .format("MM/DD/YYYY h:mm A"), the resulting formatted time will already include the DST offset if DST is in effect for that particular date and time in the user's time zone. You don't need to manually adjust for the DST offset.

Moment Timezone handles DST rules for various time zones, so as long as you provide the correct time zone identifier (userTimezone in your code), it will automatically handle the DST offset for you.

Diksha Chaudhary
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  • thanks for your response, Saves lots of my time! – programmers_view Jun 16 '23 at 12:19
  • Re: "*by chaining .tz(userTimezone), you are converting that UTC time to the user's local time*" not really. It associates the user timezone with the moment object so that subsequent operations will be in the context of that timezone. The underlying *Date* object is not modified. – RobG Jun 17 '23 at 04:18
  • @RobG What are you trying to explain? didn't get your point man, does it relate to any problem with my code snippet while converting UTC datetime string to the user's local time zone? – programmers_view Jun 19 '23 at 05:19
  • I'm trying to explain that the "UTC time" is not converted by the call to .tz, it just associates the timezone with the moment object. The formatting step calculates appropriate values based on the time zone. The underlying Date object and its time value are not altered. – RobG Jun 19 '23 at 08:51
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    Like all your other recent answers, this looks like ChatGPT – DavidW Jun 20 '23 at 06:22
  • You didn't write the answer yourself. For instance, it is impossible to learn to use [articles](https://en.wiktionary.org/wiki/article#Noun). It is plagiarism. – Peter Mortensen Jun 20 '23 at 13:15