Given that you said that, and that the problem you hit is a common pitfall for Javascript developers (especially if you're not very seasoned with the language), I'd strongly recommend picking up a copy of Douglas Crockford's Javascript: The Good Parts. Not only does he inform readers of this particular gotcha, but he also elaborates on Javascript best practices and tools that others are bringing up in their comments.
Honestly though, I've tried jslint and jshint and a bunch of other lint-like tools on the Haraka source code (google it), and it barfs all over the place for no particular reason.
"use strict" is catching a lot more errors, though frustratingly enough, not until runtime.
Javascript Patterns by Stoyan Stefanov is another great primer on JS best practices. Above all, if you're not delinting and using strict, you're dead in the water.
I think the author of the blog post understands JS scope rules. His point isn't that you shouldn't need to have a "var" in front of your declarations or that javascript is stupid and he doesn't understand it, it's that there should be a better way to find bugs like the one that bit him.
Of course, there is a way to find his particular bug (JSLint, "use strict") that he didn't know about. Still, the point about debugging being a nightmare is absolutely true.
Given that you said that, and that the problem you hit is a common pitfall for Javascript developers (especially if you're not very seasoned with the language), I'd strongly recommend picking up a copy of Douglas Crockford's Javascript: The Good Parts. Not only does he inform readers of this particular gotcha, but he also elaborates on Javascript best practices and tools that others are bringing up in their comments.