That's what I say in code reviews as well. Same for numbers.

!someValue is useful only for:

- booleans, including optional booleans (which is why every bool flag should default to false)

- undefined, null (falsy), or object/function (truthy)

It's nice for the second variant to also cover falsy NaN or things like this, for example for forms.

I guess that's where

  !!""===false

But it's this exact case that keeps tripping me up.

What about empty arrays?

Per my original comment, now I'd have to look up if

  ![]

.

So yea I agree, and extend your case to PHP "arrays" (in JS,

  !![] === true

  true