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Timezone

Timezone adds dayjs.tz .tz .tz.guess .tz.setDefault APIs to parse or display between time zones.

var utc = require("dayjs/plugin/utc");
// import utc from 'dayjs/plugin/utc' // ES 2015

var timezone = require("dayjs/plugin/timezone"); // dependent on utc plugin
// import timezone from 'dayjs/plugin/timezone' // ES 2015

dayjs.extend(utc);
dayjs.extend(timezone);

const timestamp = "2014-06-01 12:00";
const tz = "America/New_York";

const dayjsLocal = dayjs(timestamp); //assumes UTC
//dayjsLocal.toISOString() -> 2014-06-01T12:00:00.000Z
//dayjsLocal.format('YYYY-MM-DDTHH:mm:ss') -> 2014-06-01T12:00:00

const dayjsAmerica = dayjsLocal.tz(tz); //existing time treated as UTC
//dayjsAmerica.toISOString() -> 2014-06-01T12:00:00.000Z
//dayjsAmerica.format('YYYY-MM-DDTHH:mm:ss') -> 2014-06-01T08:00:00

const dayjsAmericaKeep = dayjsLocal.tz(tz, true); //existing time treated as local time
//dayjsAmericaKeep.toISOString() -> 2014-06-01T16:00:00.000Z
//dayjsAmericaKeep.format('YYYY-MM-DDTHH:mm:ss') -> 2014-06-01T12:00:00

Guessing the user timezone

dayjs.tz.guess();

Parsing in a timezone

const d1 = dayjs.tz("2013-11-18 11:55", "Asia/Taipei");
d1.format(); // => 2013-11-18T11:55:00+08:00
d1.toISOString(); // => 2013-11-18T03:55:00.000Z

Converting to a timezone

const d2 = dayjs.utc("2013-11-18 11:55").tz("Asia/Taipei");
d2.format(); // => 2013-11-18T19:55:00+08:00
d2.toISOString(); // => 2013-11-18T11:55:00.000Z

Set / reset the default timezone (used by 'tz')

// Setting the default timezone
dayjs.tz.setDefault("America/New_York");

// Resetting the default timezone to the system timezone
dayjs.tz.setDefault();

Differences to moment

Using the default timezone makes moment(dateValue) use this timezone (but moment.tz(dateValue, timezone) still requires the second parameter).

But dayjs(dateValue) always uses the local timezone, even if dayjs.tz.setDefault is used; only dayjs.tz(dateValue) (without second parameter) uses the default timezone.