Huh? `var` was not retrofitted. I distinctly remember it being there since I started learning JavaScript, like around '96. It is true that a lot of people were slack about using it, but that's just laziness, not that it wasn't there.
Sorry, what I meant was more that since we have let, there isn't any good reason to use var anymore. I definitely don't advocate the thing in this article where he eliminates var usage by littering the code with IIFEs.
It's really hard to get a declaration-free language right. Python was the biggest success to date.