date-format.js

/**
 * Format a date like YYYY-MM-DD.
 *
 * @param {string} template
 * @param {Date=} [date]
 * @return {string}
 * @license MIT
 */
function formatDate(template, date) {
  // default to today
  date = new Date(date || Date.now() - new Date().getTimezoneOffset() * 6e4);

  var specs = 'YYYY:MM:DD:HH:mm:ss'.split(':');

  return date.toISOString().split(/[-:.TZ]/).reduce(function(template, item, i) {
    return template.split(specs[i]).join(item);
  }, template);
}
// console.log(formatDate('YYYY-MM-DD')); // ↪ 2015-02-18
// console.log(formatDate('MM/DD/YYYY, HH:mm:ss')); // ↪ 02/18/2015, 19:45:31


// Return a future or past date
function anotherDay(diff, date) {
  // default to today
  date = new Date(date || Date.now() - new Date().getTimezoneOffset() * 6e4);

  // one day in seconds
  var oneDay = 24 * 60 * 60 * 1000;

  // compute the different day
  var theDay = new Date(date.getTime() + (oneDay * diff));
  if (date < 0) {
    theDay = theDay + oneDay;
  }

  return theDay;
}


console.log(anotherDay(7)); // date object one week from now
console.log(anotherDay(-2, new Date('2015-02-01T01:23:45.678Z')));
// ↪  Fri Jan 30 2015 17:23:45 GMT-0800 (PST)

function getDateString(options, date, locale) {
  // default to today and a nice US format option
  options = options || {
    weekday: 'long',
    year: 'numeric',
    month: 'long',
    day: 'numeric'
  };
  date = new Date(date || Date.now() - new Date().getTimezoneOffset() * 6e4);
  locale = locale || 'en-US';

  return date.toLocaleDateString(locale, options);
}
// var options = {
//   weekday: 'long',
//   year: 'numeric',
//   month: 'long',
//   day: 'numeric'
// };
// console.log(getDateString(options, new Date('2012-12-20T01:23:45.678Z'), 'de-DE'));
// → "Mittwoch, 19. Dezember 2012"
// an application may want to use UTC and make that visible
// options.timeZone = 'UTC';
// options.timeZoneName = 'short';
// console.log(getDateString(options, new Date('2012-12-20T01:23:45.678Z')));
// → "Thursday, December 20, 2012, UTC"