/**
 * Generates an ISO 8601 formatted date string (YYYY-MM-DD) from
 * a Date object.
 *
 * The goal is to return the value of Date.prototype.toISOString
 * without the time portion.
 * (e.g., '2023-03-21T04:15:47.000Z' becomes '2023-03-21')
 *
 * This is useful for setting a date input's min/max values
 * and also for setting date values (e.g., for automated tests).
 *
 * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/toISOString
 * @see https://developer.mozilla.org/en-US/docs/Web/HTML/Date_and_time_formats#date_strings
 * @see https://yagisanatode.com/2022/01/12/create-a-iso-string-from-date-string-input-intended-for-utc-date-in-javascript/
 * @param {Date} date
 * @returns {string}
 */
const getISOFormattedDate = (date) => {
  // First we need to get the timezone offset in milliseconds.
  // The timezone offset is the difference between the time on
  // the local computer and Universal Coordinated Time (UTC).
  const timezoneOffsetInMinutes = date.getTimezoneOffset();
  const timezoneOffsetInMilliseconds = timezoneOffsetInMinutes * 60 * 1000;

  // Now, let's convert the given date to milliseconds.
  const dateInMilliseconds = Date.parse(date);

  // Calculate the date with the timezone offset and convert to
  // ISO format (e.g., '2023-03-21T04:15:47.000Z').
  const dateWithOffset = dateInMilliseconds - timezoneOffsetInMilliseconds;
  const dateAsISOString = new Date(dateWithOffset).toISOString();

  // Split to return ISO 8601 format (YYYY-MM-DD).
  return dateAsISOString.split("T")[0];
};

console.log(getISOFormattedDate(new Date()));