JavaScript Date Assessment

Test.js

/* Assessment:
    * Native date creation -> Non-ISO will create date in current timezone
    * Native date creation -> ISO will create date in GMT timezone
    - When parsing "literal" ISO, parseISO & parseJSON are same - identical to native
    * When parsing "short" ISO, parseISO converts ISO string yyyy/mm/dd to local timezone (adds time offset) unlike native
    * formatISO should be used for converstion to date string yyyy/mm/dd?  What happens when it is converted back into a DateTime?  Assume UTC?
    * DatePicker, push in a parseISO date or ISO string, outputs a date type with HST offset
    *
  */
  describe('Date: Timezones', () => {
    // December 31, 2020 23:59:59 HST | Janurary , 2021 09:59:59 GMT | 2021-01-01T09:59:59.999Z
    systemDate = new Date(1609495199999);

    it('show native date creation with timezones into UTC standard', () => {
      // 2021-01-01T09:59:59.999Z - explict
      expect(new Date(global.Date.now()).valueOf()).toBe(1609495199999);
      expect(new Date(global.Date.now()).toISOString()).toBe('2021-01-01T09:59:59.999Z'); // UTC
      expect(new Date(global.Date.now()).toUTCString()).toBe('Fri, 01 Jan 2021 09:59:59 GMT');
      expect(new Date(global.Date.now()).toLocaleString()).toBe('12/31/2020, 11:59:59 PM');
      expect(new Date(global.Date.now()).getDate()).toBe(31); // HST Day
      expect(new Date(global.Date.now()).getUTCDate()).toBe(1); // GMT Day

      // ISO "Literal" String
      expect(new Date('2021-01-01T09:59:59.999Z').valueOf()).toBe(1609495199999);
      expect(new Date('2021-01-01T09:59:59.999Z').toISOString()).toBe('2021-01-01T09:59:59.999Z'); // UTC
      expect(new Date('2021-01-01T09:59:59.999Z').toUTCString()).toBe('Fri, 01 Jan 2021 09:59:59 GMT');
      expect(new Date('2021-01-01T09:59:59.999Z').toLocaleString()).toBe('12/31/2020, 11:59:59 PM');
      expect(new Date('2021-01-01T09:59:59.999Z').getDate()).toBe(31); // HST Day
      expect(new Date('2021-01-01T09:59:59.999Z').getUTCDate()).toBe(1); // GMT Day

      // ISO "Short" String - assumes GMT, no offset
      expect(new Date('2021-01-01').toISOString()).toBe('2021-01-01T00:00:00.000Z'); // UTC no offset
      expect(new Date('2021-01-01').toUTCString()).toBe('Fri, 01 Jan 2021 00:00:00 GMT');
      expect(new Date('2021-01-01').toLocaleString()).toBe('12/31/2020, 2:00:00 PM');
      expect(new Date('2021-01-01').getDate()).toBe(31); // HST Day
      expect(new Date('2021-01-01').getUTCDate()).toBe(1); // GMT Day

      // Non-ISO string - creates date based on current timezone (HST) - has offset
      expect(new Date('01/01/2021').toISOString()).toBe('2021-01-01T10:00:00.000Z'); // UTC, note +10 hours - HST offset
      expect(new Date('01/01/2021').toUTCString()).toBe('Fri, 01 Jan 2021 10:00:00 GMT');
      expect(new Date('01/01/2021').toLocaleString()).toBe('1/1/2021, 12:00:00 AM'); // User's Date
      expect(new Date('01/01/2021').getDate()).toBe(1); // HST Day
      expect(new Date('01/01/2021').getUTCDate()).toBe(1); // GMT Day
    });

    it('show date-fns parse into date', () => {

      // ISO Date String - outputs same as native
      const isoFullNativeUTC = new Date('2021-01-01T09:59:59.999Z').toUTCString(); // 01 Jan 2021 09:59:59 GMT
      const isoFullNativeLocale = new Date('2021-01-01T09:59:59.999Z').toLocaleString(); // 12/31/2020, 11:59:59 PM

      expect(fnsParseISO('2021-01-01T09:59:59.999Z').toUTCString()).toEqual(isoFullNativeUTC); // Fri, 01 Jan 2021 09:59:59 GMT
      expect(fnsParseISO('2021-01-01T09:59:59.999Z').toLocaleString()).toEqual(isoFullNativeLocale); // 12/31/2020, 11:59:59 PM

      expect(fnsParseJSON('2021-01-01T09:59:59.999Z').toUTCString()).toEqual(isoFullNativeUTC); // Fri, 01 Jan 2021 09:59:59 GMT
      expect(fnsParseJSON('2021-01-01T09:59:59.999Z').toLocaleString()).toEqual(isoFullNativeLocale); // 12/31/2020, 11:59:59 PM

      // ISO Date String - not same as native
      const nonIso = new Date('01/01/2021').toISOString(); // 2021-01-01T10:00:00.000Z -> Native: 2021-01-01T00:00:00.000Z
      const nonIsoUTC = new Date('01/01/2021').toUTCString(); // Fri, 01 Jan 2021 10:00:00 GMT -> Native: Fri, 01 Jan 2021 00:00:00 GMT
      const nonIsoLocale = new Date('01/01/2021').toLocaleString(); // 1/1/2021, 12:00:00 AM -> Native: 12/31/2020, 11:59:59 PM

      // Assumes local timezone HST unlike native
      expect(fnsParseISO('2021-01-01').toISOString()).toEqual(nonIso); // Same day - adds HST +10 offset
      expect(fnsParseISO('2021-01-01').toUTCString()).toEqual(nonIsoUTC); // Same day - adds HST +10 offset
      expect(fnsParseISO('2021-01-01').toLocaleString()).toEqual(nonIsoLocale); // Same day - Noon

      expect(fnsParseISO('2021-01-01').toISOString()).not.toEqual(new Date('2021-01-01').toISOString()); // Native doesn't have +10 offset
      expect(fnsParseISO('2021-01-01').toUTCString()).not.toEqual(new Date('2021-01-01').toUTCString());
      expect(fnsParseISO('2021-01-01').toLocaleString()).not.toEqual(new Date('2021-01-01').toLocaleString());
    });

    it('show date-fns format', () => {
      expect(fnsParse('2021-01-01', "yyyy-MM-dd", new Date(Date.now()))).toEqual(new Date('2021-01-01T10:00:00.000Z')); // Same as parseISO
      expect(fnsParse('01/01/2021', "MM/dd/yyyy", new Date(Date.now()))).toEqual(new Date('2021-01-01T10:00:00.000Z')); // Sam as Native
    });

    it('show date-fns format into ISO String - non-UTC', () => {
      // ISO Date String
      expect(fnsFormatISO(new Date('2021-01-01T09:59:59.999Z'))).toBe('2020-12-31T23:59:59-10:00'); // Notice it added HST Timezone (10:00)
      expect(fnsFormatISO(new Date('2021-01-01'))).toBe('2020-12-31T14:00:00-10:00'); // Same 2:00 PM HST

      // Non-ISO string - creates date based on current timezone (HST)
      expect(fnsFormatISO(new Date('01/01/2021'))).toBe('2021-01-01T00:00:00-10:00'); // User's Date

      // ISO yyyy-mm-dd string
      expect(fnsFormatISO(new Date('2021-01-01T09:59:59.999Z'), { representation: 'date' })).toBe('2020-12-31');
      expect(fnsFormatISO(new Date('2021-01-01'), { representation: 'date' })).toBe('2020-12-31');
      expect(fnsFormatISO(new Date('01/01/2021'), { representation: 'date' })).toBe('2021-01-01'); // User's Date
    });

    it('show date-fns format', () => {
      expect(fnsFormat(new Date('2021-01-01'), "yyyy-MM-dd")).toBe('2020-12-31'); // Day before - no offset
      expect(fnsFormat(fnsParseISO('2021-01-01'), "yyyy-MM-dd")).toBe('2021-01-01');
    });

    it('should show correct date for user in Hawaii from a deadline entry in California', () => {
      const date = fnsParseJSON('2021-01-01T08:08:00.000Z');
      expect(fmDate(date, 'short')).toBe('12/31/2020');
    });
  });