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

Here is an example of how this operator can be used efficiently, where it makes sense to use it:

leftOffset = -(~~$('html').css('padding-left').replace('px', '') + ~~$('body').css('margin-left').replace('px', '')),

Source:

See section Interacting with points