Variables, control structures, and functions, definitely. Operators is another big one. In particular, I think a lot of non-programmers have trouble internalizing the distinction between assignment and comparison operators. Going over logical operators also gives people a good chance to connect with programming on an intuitive level (everyone understands what "and" and "or" and "not" mean).

But since it's JavaScript, there are a couple of things you'll probably need to touch on that wouldn't necessarily be part of the "first six hours" if you were teaching a different language.

For instance*, objects. Obviously you don't want to delve too deeply into object-oriented programming theory, but it's hard to accomplish much in JavaScript without a basic understanding that elements on a page (and the page itself) are treated as "objects" and to find out their characteristics you refer to their "properties" and to make them do things you use "methods."

Also, the concept of events and event handlers is pretty fundamental.

Those are all very handy things to know about, of course, but it does give you quite a bit more to cover. Still, I think if you don't cover that stuff, they'll come away from the class still baffled by even the most basic cut-and-paste JavaScript code they'll come across.

--Kevin

Update: * Pun unintentional, but I like it.