Format date in a specific timezone

I'm using Moment.js to parse and format dates in my web app. As part of a JSON object, my backend server sends dates as a number of milliseconds from the UTC epoch (Unix offset).

Parsing dates in a specific timezone is easy -- just append the RFC 822 timezone identifier to the end of the string before parsing:

// response varies according to your timezone
const m1 = moment('3/11/2012 13:00').utc().format("MM/DD HH:mm")

// problem solved, always "03/11 17:00"
const m2 = moment('3/11/2012 13:00 -0400').utc().format("MM/DD HH:mm")

console.log({ m1, m2 })

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.24.0/moment.min.js"></script>

But how do I format a date in a specifc timezone?

I want consistent results regardless of the browser's current time, but I don't want to display dates in UTC.

Solution 1:

As pointed out in Manto's answer, .utcOffset() is the preferred method as of Moment 2.9.0. This function uses the real offset from UTC, not the reverse offset (e.g., -240 for New York during DST). Offset strings like "+0400" work the same as before:

// always "2013-05-23 00:55"
moment(1369266934311).utcOffset(60).format('YYYY-MM-DD HH:mm')
moment(1369266934311).utcOffset('+0100').format('YYYY-MM-DD HH:mm')

The older .zone() as a setter was deprecated in Moment.js 2.9.0. It accepted a string containing a timezone identifier (e.g., "-0400" or "-04:00" for -4 hours) or a number representing minutes behind UTC (e.g., 240 for New York during DST).

// always "2013-05-23 00:55"
moment(1369266934311).zone(-60).format('YYYY-MM-DD HH:mm')
moment(1369266934311).zone('+0100').format('YYYY-MM-DD HH:mm')

To work with named timezones instead of numeric offsets, include Moment Timezone and use .tz() instead:

// determines the correct offset for America/Phoenix at the given moment
// always "2013-05-22 16:55"
moment(1369266934311).tz('America/Phoenix').format('YYYY-MM-DD HH:mm')

Solution 2:

A couple of answers already mention that moment-timezone is the way to go with named timezone. I just want to clarify something about this library that was pretty confusing to me. There is a difference between these two statements:

moment.tz(date, format, timezone)

moment(date, format).tz(timezone)

Assuming that a timezone is not specified in the date passed in:

The first code takes in the date and assumes the timezone is the one passed in. The second one will take date, assume the timezone from the browser and then change the time and timezone according to the timezone passed in.

Example:

moment.tz('2018-07-17 19:00:00', 'YYYY-MM-DD HH:mm:ss', 'UTC').format() // "2018-07-17T19:00:00Z"

moment('2018-07-17 19:00:00', 'YYYY-MM-DD HH:mm:ss').tz('UTC').format() // "2018-07-18T00:00:00Z"

My timezone is +5 from utc. So in the first case it does not change and it sets the date and time to have utc timezone.

In the second case, it assumes the date passed in is in -5, then turns it into UTC, and that's why it spits out the date "2018-07-18T00:00:00Z"

NOTE: The format parameter is really important. If omitted moment might fall back to the Date class which can unpredictable behaviors

Assuming the timezone is specified in the date passed in:

In this case they both behave equally

Even though now I understand why it works that way, I thought this was a pretty confusing feature and worth explaining.