They are only talking about one javascript engine (node). They didn't test any other engine or go into the implementation in node. For all we know, this might just be a poorly optimized code path in node that needs a little love, but the author didn't bother doing any investigation.

Looking at the linked github issue, jsc doesn't have the performance penalty. It would have been interesting if the author had investigated why and shared that with us.

If this article is about hoisting then this is a well-made high-effort high-value article. If this article is about performance then this is a low-effort low-value summary of a github issue they read.