npm install dayjs
npm install dayjs-plugin-utc
npm install dayjs-plugin-timezone

const dayjs = require('dayjs');
const utc = require('dayjs/plugin/utc');
const timezone = require('dayjs/plugin/timezone');

// Extend dayjs with necessary plugins
dayjs.extend(utc);
dayjs.extend(timezone);

/**
 * Formats a given Date object into specified patterns using dayjs.
 *
 * @param {Date} date - The Date object to format.
 * @param {string} pattern - The pattern defining the output format.
 * @param {boolean} [isInputUTC=false] - (Optional) If true, treats the input date as UTC. Otherwise, uses the user's local timezone.
 * @param {string|string[]} [outputTZ] - (Optional) The timezone(s) for the output formatted date(s). Can be a single timezone string or an array of timezone strings.
 * @returns {{
 *   isValid: boolean,
 *   formattedDates: { [timezone: string]: string }
 * }} - An object containing the validity of the date and an object of formatted date strings keyed by timezone.
 *
 * @example
 * formatDate(new Date(), 'YYYY-MM-DD HH:mm'); 
 * // {
 * //   isValid: true,
 * //   formattedDates: {
 * //     'Local': "2025-01-07 09:35 AM",
 * //     'UTC': "2025-01-07 14:35 PM"
 * //   }
 * // }
 */
function formatDate(date, pattern, isInputUTC = false, outputTZ) {
  // Initialize return object
  const result = {
    isValid: false,
    formattedDates: {}
  };

  // Validate the date object
  if (!(date instanceof Date) || isNaN(date)) {
    return result; // isValid remains false, formattedDates is empty
  }

  // Validate the pattern
  if (typeof pattern !== 'string') {
    return result; // isValid remains false, formattedDates is empty
  }

  // Determine the input timezone
  const inputTZ = isInputUTC ? 'UTC' : dayjs.tz.guess();

  // Create a dayjs instance with input timezone
  let m;
  if (inputTZ === 'UTC') {
    m = dayjs.utc(date);
  } else {
    m = dayjs.tz(date, inputTZ);
  }

  // Check if the date is valid
  if (m.isValid()) {
    result.isValid = true;

    // Always include UTC
    result.formattedDates['UTC'] = m.clone().utc().format(pattern);

    // Prepare the list of additional output timezones
    let additionalTimezones = [];

    if (outputTZ) {
      if (Array.isArray(outputTZ)) {
        additionalTimezones = outputTZ;
      } else if (typeof outputTZ === 'string') {
        additionalTimezones = [outputTZ];
      } else {
        console.warn('outputTZ should be a string or an array of strings representing valid IANA timezones.');
      }
    } else {
      // Default to 'Local' if no outputTZ is specified
      additionalTimezones = ['Local'];
    }

    // Iterate over each specified output timezone and format the date
    additionalTimezones.forEach(tz => {
      let formattedDate = '';
      if (tz === 'Local') {
        const localTZ = dayjs.tz.guess();
        formattedDate = m.clone().tz(localTZ).format(pattern);
        result.formattedDates['Local'] = formattedDate;
      } else {
        // Validate the timezone
        if (dayjs.tz.zone(tz)) { // Checks if tz is a valid timezone
          formattedDate = m.clone().tz(tz).format(pattern);
          result.formattedDates[tz] = formattedDate;
        } else {
          console.warn(`Invalid timezone provided: "${tz}". Skipping this timezone.`);
        }
      }
    });
  }

  return result;
}