I think now that JS has classes, the private and static keywords/symbols are only a natural next step.
Still, I have to agree with some others about the # symbol for private. That's bizarre to me.
On the other hand though, I guess you'll get some kind of indication from outside the class that what you're trying to use is private. Hopefully it's helpful in that regard.
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.