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new Date().toISOString()

when i execute this will get output as

2022-04-03T21:13:50.049Z

i am looking to get in below format.

2022-04-03T21:13:50.049+05:30

i have only cityname with me . how can i get this GMT+"05:30" based on city?

LamriN
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    That's not possible. There are multiple cities with the same name. You need the timezone. – jabaa Apr 03 '22 at 21:27
  • To get timezone from location you need a lookup table or something like [Google Time Zone API](https://developers.google.com/maps/documentation/timezone/get-started) – Yogi Apr 03 '22 at 22:03
  • There are many posts regarding formatting dates, e.g. [*Date.toISOString() but local time instead of UTC*](https://stackoverflow.com/questions/49330139/date-toisostring-but-local-time-instead-of-utc) and [*https://stackoverflow.com/questions/17415579/how-to-iso-8601-format-a-date-with-timezone-offset-in-javascript*](https://stackoverflow.com/questions/17415579/how-to-iso-8601-format-a-date-with-timezone-offset-in-javascript). Once you have the IANA representative location, you can use *Intl.DateTimeFormat.formatToParts* to get the parts for formatting, including the offset. – RobG Apr 03 '22 at 23:12

1 Answers1

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This is a duplicate but I can't find one at the moment.

One problem is to map the city name to an IANA representative location, so "London" in the UK becomes "Europe/London", however there are many, many cities called "London" throughout the world (similarly there are cities called Hyderabad India and Pakistan).

There's a list of locations at Wikipedia, I'm pretty sure the location names are unique without the continent identifier however there are many duplicate city names in the world, e.g. Perth Scotland is not an IANA location, Perth Australia is. Similarly with many other names.

Here's a function created some time ago to use the Intl.DateTimeFormat object to create and ISO 8601 formatted timestamp based on an IANA representative location.

/* Return an ISO 8601 formatted timestamp for location on given date
 * @param {string} loc - IANA representative location to get timezone name for
 *                       "default" returns host setting
 * @param {Date} date  - date to get timezone name for
 *                       default is current date
 * @returns {string} timestamp as YYYY-MM-DDTHH:mm:ss±HH:mm
**/
function toISOByLoc(loc = 'default', date = new Date()) {
  let opts = {
    year: 'numeric',
    month: '2-digit',
    day: '2-digit',
    hour: '2-digit',
    minute: '2-digit',
    second: '2-digit',
    hour12: false
  };
  if (loc.toLowerCase() != 'default') {
    opts.timeZone = loc;
  }
  let {year, month, day, hour, minute, second, timeZoneName} = new Intl.DateTimeFormat('en', opts ).formatToParts().reduce((parts, part) => {
    parts[part.type] = part.value;
    return parts;
  }, Object.create(null));
  // Return timestamp
  return `${year}-${month}-${day}T${hour}:${minute}:${second}${getOffsetForLoc(loc, date)}`;
}

/* Return offset for location on given date
 * @param {string} loc - IANA representative location to get timezone name for
 *                       "default" returns host setting
 * @param {Date} date  - date to get timezone name for
 *                       default is current date
 * @returns {string} offset as ±HH:mm
**/
function getOffsetForLoc(loc = 'default', date = new Date()) {
  let opts = {
      hour: 'numeric',
      timeZoneName: 'short'
  }
  if (loc != 'default') {
    opts.timeZone = loc;
  }
  // Usually get UTC offset as ±H[:mm] with language fr
  let offset = date.toLocaleString('fr', opts).match(/\S+$/)[0];
  // But sometimes get abbreviation so test and use en otherwise
  if (!/\d/.test(offset)) {
    offset = date.toLocaleString('en',{
      hour: 'numeric',
      timeZone: loc,
      timeZoneName: 'short'
    }).match(/\S+$/)[0];
  }
  // Build offset string and return
  let sign = /\+/.test(offset)? '+' : '-';
  let [offH, offM] = offset.match(/\d+/g) || '0';
  return `${sign}${offH.padStart(2,'0')}:${offM || '00'}`;
}

// Examples with default date (now)
['Asia/Kolkata',
 'America/New_York',
 'Pacific/Kiritimati'
].forEach(loc => console.log(
 `${loc}: ${toISOByLoc(loc)}`
));
RobG
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