@es-labs/node/iso/datetime.js

Reusable library

/**
 * Get array of strings with datetime elements after offseting input date by X days
 * @param {string} isoString - ISO datetime string
 * @param {Number} days - ISO datetime string
 * @returns {string[]}} -  return array or YYYY, MM, DD strings - not so useful...
 */
export const dateStrAddDay = (dateStr, days = 0) => {
  const d = new Date(Date.parse(dateStr) - new Date().getTimezoneOffset());
  d.setDate(d.getDate() + days); // add the days
  return [d.getFullYear().toString(), (d.getMonth() + 1).toString().padStart(2, 0), d.getDate().toString().padStart(2, 0)];
}

/**
 * Get new ISO datetime string date after offseting input date by X days
 * @param {string} isoString - ISO datetime string
 * @param {Number} days - ISO datetime string
 * @returns {string} -  return ISO datetime string
 */
export const dateStrAddDayISO = (isoString, days = 0) => {
  const d = new Date(isoString);
  d.setDate(d.getDate() + days);
  return d.toISOString();
}

/**
 * Get local,date time and TZ in ISO format
 * @param {Date|string} dt - Date object or ISO datetime string
 * @param {string} tz - IANA time zone name, e.g. 'Asia/Singapore'
 * @returns {string} -  return string format: 2023-10-24 11:40:15 GMT+8
 */
export const getLocaleDateTimeTzISO = (dt, tz) => {
  const opts = {
    timeZoneName: 'short',
    hour12: false,
    year: 'numeric',
    month: '2-digit',
    day: '2-digit',
    hour: '2-digit',
    minute: '2-digit',
    second: '2-digit',
  }
  if (tz) opts.timeZone = tz;
  if (!(dt instanceof Date)) dt = new Date(dt);
  return dt.toLocaleString('sv', opts);
}

/**
 * Get local date in ISO format
 * @param {string} isoString - ISO datetime string
 * @param {string} tz - IANA time zone name, e.g. 'Asia/Singapore'
 * @returns {string}
 */
export const getLocaleDateISO = (isoString, tz) => getLocaleDateTimeTzISO(isoString, tz).substring(0, 10);

/**
 * Get local date in ISO format
 * @param {string} isoString - ISO datetime string
 * @param {string} tz - IANA time zone name, e.g. 'Asia/Singapore'
 * @returns {string}
 */
export const getLocaleTimeISO = (isoString, tz) => getLocaleDateTimeTzISO(isoString, tz).substring(11, 19);

/**
 * Get timezone offset in ISO format (+hh:mm or -hh:mm)
 * @param {Date|undefined} date - if undefined, will create a date object and use that timezone 
 * @returns {string}
 */
export const getTzOffsetISO = (date) => {
  const pad = n => `${Math.floor(Math.abs(n))}`.padStart(2, '0'); // Pad a number to 2 digits
  if (!date) date = new Date();
  const tzOffset = -date.getTimezoneOffset();
  return (tzOffset >= 0 ? '+' : '-') + pad(tzOffset / 60) + ':' + pad(tzOffset % 60);
};

/**
 * Get return current UTC timestamp YmdHms
 * @param {Date|undefined} date - if undefined, will create a date object and use that timezone 
 * @returns {string} YYYYMMDD_HHmmssZ
 */
export const getYmdhmsUtc = (date) => {
  if (!date) date = new Date();
  const d = date.toISOString();
  return d.substring(0,4) + d.substring(5,7) + d.substring(8,10) + '_' + d.substring(11,13) + d.substring(14,16) + d.substring(17,19) + 'Z';
}

/**
 * Get day of week index (0-6) for a given date and timezone
 * @param {Date|string} date - Date object or ISO datetime string
 * @param {string} tz - IANA time zone name, e.g. 'Asia/Singapore'
 * @returns {Number}
 */
export const getDayOfWeek = (date, tz) => {
  if (!(date instanceof Date)) date = new Date(date)
  const opts = { weekday: 'short' }
  if (tz) opts.timeZone = tz
  const shortDayName = new Intl.DateTimeFormat('en-US', opts).format(date) // Get short day name string for specified timezone  
  const daysOfWeek = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'] // Map the short name back to a numeric index
  return daysOfWeek.indexOf(shortDayName);
}

// Obsolete use getLocaleDateISO and getLocaleTimeISO instead
// export const dateISO = (date) => new Date(date.getTime() - date.getTimezoneOffset() * 60000).toISOString().substring(0, 10);
// export const timeISO = (date) => new Date(date.getTime() - date.getTimezoneOffset() * 60000).toISOString().substring(11, 19);