Changes the format of a string-date

formatDate.js

/**
 * Changes the format of a string-date.
 *
 * @param  {Object | String} options: it can be a String with the date, or an Object with the following properties:
 *         - {String} date: the entry date to change the format
 *         - {String} inputFormat: the format of the entry date
 *         - {String} outputFormat: the format of the output date
 * @return {String}
 */
const formatDate = (() => {
  const _YMD = (/[yMd]+/gi);
  const _Y = (/y+/);
  const _M = (/M+/);
  const _D = (/d+/);

  const defaults = {
    date: null,
    inputFormat: 'yyyy/MM/dd',
    outputFormat: 'MM/dd/yyyy',
  };

  return (options) => {
    let d, m, y; // eslint-disable-line
    if (typeof options === 'string') {
      options = { date: options };
    }
    const opt = Object.assign({}, defaults, options);
    const dateParts = opt.date.split(/\D/);
    const formatParts = opt.inputFormat.split(/\W/);
    for (let i = 0; i < formatParts.length; i += 1) {
      if (_Y.test(formatParts[i])) { y = dateParts[i]; continue; }
      if (_M.test(formatParts[i])) { m = dateParts[i]; continue; }
      if (_D.test(formatParts[i])) { d = dateParts[i]; continue; }
    }
    return opt.outputFormat.replace(_YMD, (match) => { // eslint-disable-line
      if (_Y.test(match)) return y;
      if (_M.test(match)) return m;
      if (_D.test(match)) return d;
    });
  };
})();

usage.js

var date = '2016/06/30';
// default inputFormat: 'yyyy/MM/dd'
// default outputFormat: 'MM/dd/yyyy'
var output = formatDate(date);

console.log(date, '->', output);
// expected:
// 2016/06/30 -> 06/30/2016

//-----------------------------------
date = '1995-12-17T03:24:59-05:00';
output = formatDate({
  date,
  inputFormat: 'yyyy-MM-dd',
  outputFormat: 'dd/MM/yyyy'
});

console.log(date, '->', output);
// expected:
// 1995-12-17T03:24:59-05:00 -> 17/12/1995

Great!