local-iso-dt/index.mjs

Convert the most common types of dates into ISO8601/RFC3339-formatted YYYY-MM-DDTHH:MM:SS strings in the local timezone

/**
 * Convert the most common types of dates to the ISO8601/RFC3339 format,
 * in the local time zone, without milliseconds.
 *
 * @param {Date|number|string} [d = Date.now()] - the date, either a Date object,
 *   or a UNIX timestamp in (milli/micro/nano)seconds
 * @return {String} ISO8601/RFC3339 `YYYY-MM-DDTHH:MM:SS` string in the local timezone
 */
export function localISOdt(d) {
    if (!d)
        d = new Date();
    if (/^\d\d\d\d-\d\d-\d\d/.test(d))
        return d; // leave YYYY-MM-DD strings unchanged
    if (/^\d+\.?\d*$/.test(d)) {
        // We have a (possibly fractional) number. Date takes a millisecond argument, so
        if (d < 4102512345)
            d *= 1000; // ...interpret as seconds if before 1/1/2100
        if (d > 4102512345000)
            d /= 1000; // ...and as microseconds if after 1/1/2100
        if (d > 4102512345000)
            d /= 1000; // ...and finally as nanoseconds
    }
    if (!(d instanceof Date))
        d = new Date(d); // parse it
    return new Date(d.getTime() - d.getTimezoneOffset() * 60000) // the offset is in minutes
        .toISOString().slice(0, -5); // drop the .milliseconds and 'Z';
}