Date to ISO format with timezone

OSCC · JavaScript, Date · Oct 13, 2021

Converts a date to extended ISO format (ISO 8601), including timezone offset.

  • Use Date.prototype.getTimezoneOffset() to get the timezone offset and reverse it. Store its sign in diff.
  • Define a helper function, pad(), that normalizes any passed number to an integer using Math.floor() and Math.abs() and pads it to 2 digits, using String.prototype.padStart().
  • Use pad() and the built-in methods in the Date prototype to build the ISO 8601 string with timezone offset.
const toISOStringWithTimezone = date => {
  const tzOffset = -date.getTimezoneOffset();
  const diff = tzOffset >= 0 ? '+' : '-';
  const pad = n => `${Math.floor(Math.abs(n))}`.padStart(2, '0');
  return date.getFullYear() +
    '-' + pad(date.getMonth() + 1) +
    '-' + pad(date.getDate()) +
    'T' + pad(date.getHours()) +
    ':' + pad(date.getMinutes()) +
    ':' + pad(date.getSeconds()) +
    diff + pad(tzOffset / 60) +
    ':' + pad(tzOffset % 60);
};
toISOStringWithTimezone(new Date()); // '2020-10-06T20:43:33-04:00'

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