Formatting dates/times in node.js using Olson timezones and moment.js. Converts server-side timestamps to the browser's timezone.

date-util.js

var moment = require('moment');
var tz = require('timezone/loaded');
var time = require('time');  

module.exports = function() {
  var strftime_format = '%F %T %z'; // used to convert a date into a normalized strftime format with timezone
  var moment_format = 'YYYY-MM-DD HH:mm:ss zz'; // moment.js LDML format for parsing date strings

  /**
   * Convert a Javascript Date into node-time wrapper with the appropriate timezone.
   * @param date     {Date}   Javascript Date object
   * @param timezone {String} Olson timezone for this date (e.g. 'America/New_York')
   * @return node-time object with the appropriate timezone
   */
  var to_local = function(date, timezone) {
    var tz_date = new time.Date(date);
    tz_date.setTimezone(timezone); // localize the date into the specified timezone     
    return local_datetime = tz(tz_date, strftime_format, timezone); // localized format w timezone offset
  }

  /**
   * Convert a Javascript Date into a Moment.js moment obj with the appropriate timezone.
   * Using the returned moment, you can call for example 'moment.calendar()' to get a
   * human readable relative time such as 'last Friday at 3:52 PM'.
   * @param date     {Date}   Javascript Date object
   * @param timezone {String} Olson timezone for this date (e.g. 'America/New_York')
   * @return moment with the appropriate timezone
   */
  var to_moment = function(date, timezone) {
    var local_datetime = to_local(date, timezone);
    return moment(local_datetime, moment_format);
  }

  return {
    to_local: to_local,
    to_moment: to_moment
  }
}

gistfile1.md

How To Use

Read the user's timezone (Olson format) from their web browser using jstz (https://bitbucket.org/pellepim/jstimezonedetect), and set it on a hidden login form input:

$('input#timezone').val( jstz.determine().name() );

Pass the timezone to node.js in aforementioned hidden form input on the login form.

<input type="hidden" name="timezone" id="timezone">

Store the timezone in the user's express session in their login POST route:

req.session.timezone = req.body.timezone;

Then format a stored Date to the user's timezone with moment.js's nice human readable relative calendar function (based on the date-util file in this gist):

date_util.to_moment(date, timezone).calendar();

The output looks like: 'last Friday at 3:52 PM' if this happened last Friday at 3:52 PM PST. Someone in New York would see 'last Friday at 6:52 PM'.