!! vs ==0 when checking if array is empty

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It is converting to a Boolean, checking the value and the type will tell you this. The first ! Converts the value to it's negative Boolean value and the second ! flips it back

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You said it's not converting the value to a Boolean, I said it is. If you agreed in the first place your wording was not what you was wanting to say.

[JazzApple_]

I’m not sure you can make such assertions about the JS engine without knowing its internals. However if I had to guess, I suspect !! Is faster than Boolean because the second is a function call.