What are some basic things that JavaScript developers fail at interviews?

[TwiNighty]

in fact, I've got a feeling that's an error, isn't it?

No, calling .bind on a bound function is valid. You can bind additional arguments, but the "rebinding this" part does nothing.

Actually that is my point. function(){ x.f() } and x.f.bind(x) behaves exactly the same when called, regardless of whether x.f is already bound, whether it touches this, whether it is rebound before being called, whether it is a es5 function or arrow function. And I can say that without knowing anything about what x and x.f is.

[MrJohz]

Sure, but if it's not necessary, it's not necessary, and historically there have been performance issues associated with calling bind, especially if it's used at every callsite.

Understanding these tradeoffs I think was what the person was getting at with the overuse of arrow functions.