[mekoka]

Indeed. Lots of "it makes sense in the context of JavaScript" reactions here. If the article had pointed to warts in another language, we would probably have had the same reaction from proponents of that language. I think the point of the article is actually being reinforced here, as it illustrates the mindset of people who know a language so well, that they think it worthless to spend time addressing such warts when teaching it. But a programming language is not in its own universe where it is exempted from data structure theory. A[-1] in the context of a list is a convenient alias for A[len(A)-1]. When you advertise your data structure as a List or Array, but it starts to display Hashmap properties, it is confusing, in any language.