freeCodeCamp/api-server/server/utils/date-utils.js

import moment from 'moment-timezone';

// day count between two epochs (inclusive)
export function dayCount([head, tail], timezone = 'UTC') {
  return Math.ceil(
    moment(
      moment(head)
        .tz(timezone)
        .endOf('day')
    ).diff(
      moment(tail)
        .tz(timezone)
        .startOf('day'),
      'days',
      true
    )
  );
}