Here is the code. This too, a large portion of it. I'm not associated with any organization, I'm just trying to create a Chrome Extension that I will post to the Chrome Web Store and expect people to install for their own use. One of the aforementioned links contains another link to GoJS's licensing agreement. I think the answer to my question is can be found there, but I need help understanding it.
The code you first link to starts
/* Copyright (C) 1998-2019 by Northwoods Software Corporation. All Rights Reserved. */, but as I have noted here this is a historical hangover with no modern function save to really complicate the licensing position of content. It is, however, a harbinger of bigger licensing issues to come.
Turning to the project's actual licence file, we find it not only written in HTML, but HTML made by MS Word; both of these are bad signs. The licence when viewed makes much (worrying) reference to License Certificates and Evaluation Licenses, and goes on to say that:
2.1.4 Except as may otherwise expressly be permitted by this Agreement, and subject to such additional limitations and restrictions as are set forth in this Agreement, Customer may not:
(a) use, copy, display, publish, or transfer any Licensed Product;
(b) modify any Licensed Product, or create any derivative work of any Licensed Product;
This is not free software. I'm guessing it was never intended to be. It's a commercial company's commercial source, and in a popular modern form of stupidity they have decided to do their development out in the open on a public
You cannot lawfully use this content. Worse, by even reading it in detail you risk opening yourself up to accusations of any similar work you later write being a derivative, and thus unusable.