Using javascript file as third party library

Hi all,
I am trying to use webgazer.js, a an eye-tracking library that comes as a single javascript file.

Following a bit of research online, I added the script to the src/assets/js/ directory and added the webgazer.js file as a script in the index.html of my app (within <head>):

<script async src="./assets/js/webgazer.js" type="text/javascript"></script>

I then created a page using

ionic g page test-eye-tracking-page

and used the webgazer object in test-eye-tracking-page.ts:

export class TestEyeTrackingPage {

    constructor(public navCtrl: NavController, public navParams: NavParams) {}
    ionViewDidEnter() {
	//start the webgazer tracker
	webgazer.begin() 
    }

When visiting the eye tracking test page, I get the error webgazer is undefined

Alternatively, I tried to use webgazer.js as a third party module, since the gitHub repo contains a package.json file.
Following the documentation, I added webgazer as a dependency

npm install github:brownhci/WebGazer --save

There is now a node_modules/webgazer/ repository. I then built the webgazer.js file and added it in nodes_modules/webgazer/.

Using the library in test-eye-tracking-age.ts

import * as webgazer from 'webgazer'

or

import 'webgazer'

leads to 'webgazer is undefined'.

Any advice on how to use the webgazer library ?