Note that the article is talking about licensing. Whether or not your JS code is 'free' depends on the license you've applied to it. In the case of sites that use things like Angular or React the user knows that code isn't using a permissive, open license, so the folk at GNU are attempting to block the code coming from the server, inject their own code that does the same thing but more freely, and still have a working version of your site. It's an interesting idea albeit perhaps incredibly not-useful if you don't care deeply about software licenses.