JS ecosystem is pretty well know for changing very fast compared to other mainstream languages. This is a fair point, NPM could implement the local cache without (hopefully) breaking anything
From my understanding they’ve always had one, but until npm@5 it wasn’t safe for concurrent access (side note: Maven still isn’t) and was prone to corruption. I think they’re making their way toward true offline cacheing a-la yarn, if they haven’t done so already.
