For 2.0, GoJS has undergone a rewrite into TypeScript. A source license will include .ts source files as well as .js sources, and examples of how to build the library into your project with Webpack or Browserify, should you wish to. This will allow you to remove unused modules from the source code, such as Layouts, Models, and Tools that you are not using.
The main library has been reduced by removing many of the uncommon figures. These are now an extension.
GoJS can now also be loaded as an ES6 Module, and can be run DOM-less in Node.
We have also added the ability to create your own Panels, with the new PanelLayout class. See an example here.
Read about these and several other changes, here: GoJS Change Log
You can access the alpha, here: GoJS - Build Interactive Diagrams for the Web