The 80 character line limit spawns from the days of screens without a lot of real estate. Now it's just like that for readability, and so it's possible to have two (or more) different code files opened side-by-side, without having to scroll to see each of them.
Those reasons still apply to HTML and JavaScript, although, it's obviously not necessary to comply with them. So it's up to you.
I agree that with HTML it can be difficult to keep within that limit, although with JavaScript it shouldn't be a problem.
