[1] Yes, classes. As in: You can never misspell an object property and have that mistake make it into production (&c for lots of other types of bugs). Plus, you get automatic refactoring you can actually rely on. Now, your JS devs may not appreciate that, but I suspect that's just because they're inexperienced and/or haven't actually worked in a good[2] statically typed language. There's also the fact that we (as humans) unconsciously try to minimize our own mistakes; "oh well, it was just a typo and we fixed it quickly!" and for most of us mistakes tend to fade quickly from memory... thus leading to a very biased view of one's own development practices which doesn't take into account how many mistakes you really make.

[2] I'm going to do a D. F. Wallace here[3].

[3] ... and say that Scala isn't great as languages go[5], but I'll bet you it's a hell of a lot better than any statically typed language your typical JS devs have any experience with[4]. One particular gripe of mine is that they still permit "null", but that's because of Java compatibility. (Oh, how much better Scala could have been without Java compatibility.)

[4] ... which would obviously colour their perception of the trade-offs between static type checking and "verbosity", "bondage & discipline", etc.

[5] It is good, though.

I think that's enough footnotes for now.

EDIT: Sorry, I lied. Added another footnote. Really doing the DFW thing, but in Reel Time(TM).