Question 276807 in Javascript Question posted in
A very good W3school tutorial can be found here.

How to find Unix timestamp of a given calendar date and time in a specific time zone in Javascript?

With APIs like Intl, I can obtain the date and time of any Unix timestamp in any time zone. How can I do the reverse?

I’d like to be able to convert any particular triplet of <calendar-date> (YYYY-MM-DD), <local-time> (HH:MM:SS), and <time-zone> (IANA timezone) (which do not necessarily correspond with fixed timezone offsets) to a Unix timestamp. I am not looking to just convert the current timestamp (which is trivial) or looking for solutions that presuppose I have a Javascript Date object; what we have is only the calendar date, local time, and time zone.

Solutions such as adding time zone offsets do not work reliably (eg in cases of DST). I had hoped Intl allowed for easy calculation of this problem.

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2

Answers


  1. 0

    Does this work for you?

    It was not trivial

    /**
 * Converts a calendar date and local time to a Unix timestamp.
 *
 * @param {string} calendarDate - The calendar date in the format 'YYYY-MM-DD'.
 * @param {string} localTime - The local time in the format 'HH:mm:ss'.
 * @param {string} timeZone - The IANA time zone identifier.
 * @returns {number} The Unix timestamp in seconds.
 */
const convertToUnixTimestamp = (calendarDate, localTime, timeZone) => {
  const [hourStr, minuteStr, secondStr] = localTime.split(':');
  let hour = parseInt(hourStr, 10);
  const minute = parseInt(minuteStr, 10);
  const second = parseInt(secondStr, 10);

  const dateTimeString = `${calendarDate}T00:00:00`;

  // Set the locale to 'en-US' for consistent formatting
  const dtf = new Intl.DateTimeFormat('en-US', {
    year: 'numeric',
    month: '2-digit',
    day: '2-digit',
    hour: '2-digit',
    minute: '2-digit',
    second: '2-digit',
    timeZoneName: 'short',
    timeZone
  });

  // Format the date portion of the datetime string
  const formattedDate = dtf.format(new Date(dateTimeString));

  // Determine if it's in the afternoon based on the hour
  const isAfternoon = hour >= 12;

  // Replace "AM" or "PM" without appending when needed
  const formattedDateTime = formattedDate.replace(
    /(AM|PM)/,
    isAfternoon ? 'PM' : 'AM'
  );

  // Subtract 12 from the hour if it's in the afternoon (PM)
  if (isAfternoon) {
    hour -= 12;
  }

  // Combine the formatted date with the provided local time
  const formattedDateTimeWithTime = formattedDateTime.replace(
    /d{2}:d{2}:d{2}/,
    `${hour.toString().padStart(2, '0')}:${minuteStr}:${secondStr}`
  );
  
  // Create a Date object with the formatted datetime string
  const date = new Date(formattedDateTimeWithTime);
  console.log(formattedDateTimeWithTime, "->", date);

  // Get the Unix timestamp in seconds
  const unixTimestamp = Math.floor(date.getTime() / 1000);
  return unixTimestamp;
};

// Example usages:
const calendarDate = '2023-04-15';

let timeZone = 'America/New_York'; 
let localTime = '00:30:00'; // Example with '00'
let unixTimestamp = convertToUnixTimestamp(calendarDate, localTime, timeZone);
console.log(unixTimestamp);

localTime = '15:30:00'; // Example with military time
unixTimestamp = convertToUnixTimestamp(calendarDate, localTime, timeZone);
console.log(unixTimestamp);

timeZone = 'Europe/Amsterdam'; // another IANA timezone
localTime = '15:30:00';
unixTimestamp = convertToUnixTimestamp(calendarDate, localTime, timeZone);
console.log(unixTimestamp);
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  2. 0

    Does the Luxon version work for you?

    // const { DateTime } = require('luxon');

// Define your input values
const calendarDate = '2023-04-15';
const localTime = '12:30:00';
const timeZone = 'America/New_York'; // Example timezone, replace with your desired IANA timezone

// Combine calendar date and local time
const dateTimeString = `${calendarDate}T${localTime}`;

// Create a Luxon DateTime object in the specified timezone
const luxonObj = luxon.DateTime.fromISO(dateTimeString, { zone: timeZone }); // remove luxon. if you have required DateTime
console.log(luxonObj)
// Get the Unix timestamp
const unixTimestamp = luxonObj.toSeconds();

console.log(unixTimestamp);
    <script src="https://cdnjs.cloudflare.com/ajax/libs/luxon/3.4.3/luxon.min.js"></script>
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