The problem is, that not everyone works on greenfield applications all the time. I never inherited modular, well tested javascript projects.
I did, on the other hand, have to take over cobbled together jQuery, Backbone and Coffeescript applications.
I think the real problem is that this has nothing to do with the article on hand.
Yahoo is writing a greenfield application, and they are avoiding exactly those problems by using React. So, literally your pain point is exactly what they are writing about avoiding, and yet you still comment on this article with the same anti-JS nonsense.
Given JS has first-class functions, and many libraries to follow functional patterns. You can write very stable code, with almost no chance of side effects within a given function/context.