There are two interfaces for using time zones with Moment.js., String) does parsing in given time zone

It takes all the same arguments as the moment constructor, but uses the last argument as a time zone identifier:

var a ="2013-11-18 11:55", "Asia/Taipei");
var b ="2013-11-18 11:55", "America/Toronto");

a.format(); // 2013-11-18T11:55:00+08:00
b.format(); // 2013-11-18T11:55:00-05:00

a.utc().format(); // 2013-11-18T03:55Z
b.utc().format(); // 2013-11-18T16:55Z

Note that created moments have different UTC time because these moments were created in different time zones.

moment().tz(String) does converting to provided time zone

var a = moment.utc("2013-11-18 11:55").tz("Asia/Taipei");
var b = moment.utc("2013-11-18 11:55").tz("America/Toronto");

a.format(); // 2013-11-18T19:55:00+08:00
b.format(); // 2013-11-18T06:55:00-05:00

a.utc().format(); // 2013-11-18T11:55Z
b.utc().format(); // 2013-11-18T11:55Z

In this example, you first create moment.utc("2013-11-18 11:55") object in UTC, and then change its timezone to specified. This also works if you create the object in your default timezone: moment("2013-11-18 11:55").

Note that created moments have equal UTC time because these moments were created in a default timezone.