typeof(NaN) == 'number'

NaN stands for 'Not a Number' but as you can see it is a 'number' nonetheless.

null is a value that isn't anything.

undefined is a value that isn't even that.

A variable can be both defined and have a value of undefined at the same time.

boolean("0") = true

boolean("false") = true

+"42" = 42

!! produces a boolean

All of the above have been taken from the following video tutorial.