DayJS Zoned

dayjs-zoned.d.ts

import { Dayjs, PluginFunc, ConfigType } from 'dayjs';

declare const plugin: PluginFunc;
export = plugin;

declare module 'dayjs' {
  /** Similar to date-fns/utcToZonedTime */
  function utcToZoned(config: ConfigType, timezone?: string): Dayjs;

  /** Similar to date-fns/zonedTimeToUtc */
  function zonedToUtc(config: ConfigType, timezone?: string): Dayjs;

  /**
   * Will change timezones, but keep the same day/month/year hours:minutes,
   * by adding or subtracting the difference between the `config` on `oldTimezone` and `newTimezone`
   */
  function changeZoneKeepTime(
    config: ConfigType,
    oldTimezone: string,
    newTimezone: string
  ): Dayjs;
}

dayjs-zoned.js

export default (_, Dayjs, dayjs) => {
  dayjs.utcToZoned = function utcToZoned(config, timeZone) {
    const date = dayjs(config);
    if (!timeZone) return date;
    const zonedString = date.toDate().toLocaleString('en-US', { timeZone });
    return dayjs(zonedString);
  };

  dayjs.zonedToUtc = function zonedToUtc(config, timeZone) {
    const utcDate = dayjs(config);
    if (!timeZone) return utcDate;
    const zonedDate = dayjs.utcToZoned(config, timeZone);
    const diff = utcDate.diff(zonedDate, 'hour');
    return utcDate.add(diff, 'hour');
  };

  dayjs.changeZoneKeepTime = function changeZoneKeepTime(
    config,
    oldTimeZone,
    newTimeZone
  ) {
    const utcDate = dayjs(config);
    if (!oldTimeZone || !newTimeZone) return utcDate;
    const oldDate = dayjs.utcToZoned(config, oldTimeZone);
    const newDate = dayjs.utcToZoned(config, newTimeZone);
    const diff = oldDate.diff(newDate, 'hour');
    return utcDate.add(diff, 'hour');
  };
};

dayjs-zoned.spec.ts

import dayjs from 'dayjs';
import plugin from './dayjs-zoned';
dayjs.extend(plugin);

// This test does not work inside Electron. See https://github.com/cypress-io/cypress/issues/1043
describe('utcToZoned', () => {
  it('works with strings', () => {
    assert.equal(
      dayjs.utcToZoned('2019-11-10T18:00:16.000Z', 'America/Sao_Paulo').toISOString(),
      '2019-11-10T14:00:16.000Z'
    );

    assert.equal(
      dayjs.utcToZoned('2019-11-10T19:00:16.000Z', 'America/Sao_Paulo').toISOString(),
      '2019-11-10T15:00:16.000Z'
    );
  });

  it('works with Dates', () => {
    assert.equal(
      dayjs
        .utcToZoned(new Date('2019-11-10T18:00:16.000Z'), 'America/Sao_Paulo')
        .toISOString(),
      '2019-11-10T14:00:16.000Z'
    );

    assert.equal(
      dayjs
        .utcToZoned(new Date('2019-11-10T19:00:16.000Z'), 'America/Sao_Paulo')
        .toISOString(),
      '2019-11-10T15:00:16.000Z'
    );
  });
});

describe('zonedToUtc', () => {
  it('works with strings', () => {
    assert.equal(
      dayjs.zonedToUtc('2019-11-10T18:00:16.000Z', 'America/Sao_Paulo').toISOString(),
      '2019-11-10T22:00:16.000Z'
    );

    assert.equal(
      dayjs.zonedToUtc('2019-11-10T19:00:16.000Z', 'America/Sao_Paulo').toISOString(),
      '2019-11-10T23:00:16.000Z'
    );
  });

  it('works with Dates', () => {
    assert.equal(
      dayjs
        .zonedToUtc(new Date('2019-11-10T18:00:16.000Z'), 'America/Sao_Paulo')
        .toISOString(),
      '2019-11-10T22:00:16.000Z'
    );

    assert.equal(
      dayjs
        .zonedToUtc(new Date('2019-11-10T19:00:16.000Z'), 'America/Sao_Paulo')
        .toISOString(),
      '2019-11-10T23:00:16.000Z'
    );
  });
});

describe('changeZoneKeepTime', () => {
  it('Converts NYC to AMS', () => {
    const americaNewYorkInUTC = '2019-10-31T02:00:00.000Z'; // 10 pm
    const europeAmsterdamInUTC = '2019-10-30T21:00:00.000Z'; // 10 pm

    assert.equal(
      dayjs
        .changeZoneKeepTime(americaNewYorkInUTC, 'America/New_York', 'Europe/Amsterdam')
        .toISOString(),
      europeAmsterdamInUTC
    );
  });

  it('Converts AMS to SP', () => {
    const europeAmsterdamInUTC = '2019-10-30T13:00:00.000Z'; // 2 pm
    const americaSaoPauloInUTC = '2019-10-30T17:00:00.000Z'; // 2 pm

    assert.equal(
      dayjs
        .changeZoneKeepTime(europeAmsterdamInUTC, 'Europe/Amsterdam', 'America/Sao_Paulo')
        .toISOString(),
      americaSaoPauloInUTC
    );
  });

  it('Converts SP to AMS', () => {
    const americaSaoPauloInUTC = '2019-10-30T12:00:00.000Z'; // 9 am
    const europeAmsterdamInUTC = '2019-10-30T08:00:00.000Z'; // 9 am

    assert.equal(
      dayjs
        .changeZoneKeepTime(americaSaoPauloInUTC, 'America/Sao_Paulo', 'Europe/Amsterdam')
        .toISOString(),
      europeAmsterdamInUTC
    );
  });

  it('Does nothing AMS to AMS', () => {
    const europeAmsterdamInUTC = '2019-10-30T10:00:00.000Z'; // 11 am

    assert.equal(
      dayjs
        .changeZoneKeepTime(europeAmsterdamInUTC, 'Europe/Amsterdam', 'Europe/Amsterdam')
        .toISOString(),
      europeAmsterdamInUTC
    );
  });

  it('Does nothing AMS to BERL', () => {
    const europeAmsterdamInUTC = '2019-10-30T10:00:00.000Z'; // 11 am

    assert.equal(
      dayjs
        .changeZoneKeepTime(europeAmsterdamInUTC, 'Europe/Amsterdam', 'Europe/Berlin')
        .toISOString(),
      europeAmsterdamInUTC
    );
  });
});