JavaScript function to generate an ISO 8601 or RFC 3339 timestamp. MIT licence.

isoTimeStamp.js

function isoTimeStamp(date, options = {}) {
  console.log(options)
  let defaults = {
    date_time: 'T',
    time_offset: ''
  }
  Object.assign(options, Object.assign(defaults, options));
  console.log(options)
  const year = date.getFullYear();
  const month = String(date.getMonth()).padStart(2, '0');
  const day = String(date.getDate()).padStart(2, '0');
  const hour = String(date.getHours()).padStart(2, '0');
  const minute = String(date.getMinutes()).padStart(2, '0');
  const second = String(date.getSeconds()).padStart(2, '0');
  const millisecond = String(date.getMilliseconds()).padStart(3, '0');
  const offset = Number(date.getTimezoneOffset());
  const offset_sign = offset >= 0 ? '-' : '+';
  const offset_hour = String(Math.abs(Math.floor(offset / 60))).padStart(2, '0');
  const offset_minute = String(Math.abs(offset % 60)).padStart(2, '0');
  return `${year}-${month}-${day}${options.date_time}${hour}:${minute}:${second}.${millisecond}${options.time_offset}${offset_sign}${offset_hour}:${offset_minute}`;
}