What does ~~ (“double tilde”) do in Javascript?

Question

I was checking out an online game physics library today and came across the ~~ operator. I know a single ~ is a bitwise NOT, would that make ~~ a NOT of a NOT, which would

Answer 1

Given ~N is -(N+1), ~~N is then -(-(N+1) + 1). Which, evidently, leads to a neat trick.