How to activate Javascript timezone support

Question

I'm trying to have a page with various analog clocks of different timezones. I know I can do it manually with offset, but as I understand the support has all the data ready including the DST. I went through this GitHub guide

So after I add the date.js file and link it to the website, as well the timezone data (olson/tzdata2018g.tar), there are two things I'm not sure about:

1. for making the files available I did this (in the jQuery file):

timezoneJS.timezone.zoneFileBasePath = 'js/timezone-js/src';

timezoneJS.timezone.init({ callback: cb });

And the callback gives me an error:

Uncaught ReferenceError: timezoneJS is not defined

2. Then, let's say the data is availabe, is this date snipped enough to get a timezone?

var dt = new timezoneJS.Date('10/31/2008', 'America/New_York');

Thanks