How To Display Timezone Offset In Dropdown

I have a dropdown of list of countries. When I select a country I load the list of timezones in a separate dropdown below.See image

I need to display the UTC offset alongside the timezone region. How do I use moment.timezone in javascript to achieve that?

Looks like you can do something like this:

If you want to get the offset at a certain date to account for daylight savings time:

var zone = moment.tz.zone('America/New_York');
zone.parse(Date.UTC(2012, 2, 19, 8, 30)); // 240 (minutes)

If you want to get the offset of a timezone given a UTC timestamp:

moment.tz.zone('America/Los_Angeles').offset(1388563200000); // 480

Source: http://momentjs.com/timezone/docs/#/zone-object/parse/