Some time ago I first stumbled upon this operator in a jQuery-plugin, which left me with a big questionmark. "~~" as in
var a = ~~b;
I know "!!" for being a doubled negation, which is essentially just a cast to boolean. Might this be something similiar? Yes it is. "~" is the bitwise negation of a value, so "~~" again is a doubled negation, flipping the ones and zeroes of a value back and forth.
This in itself is fairly unspectacular, weren't it for this implicit magic happening under the surface. The "~~"-operator effectively produces a real integer from almost every value, including NaN, null, undefined and such. Those non-values all result in a 0. Apart from that "~~" works like a Math.floor or Math.ceil, always moving in the direction of 0. So, some examples:
~~(2/0) = 0
~~Infinity = 0
~~(-2.9) = -2
~~3.4 = 3
All in all I don't know if i would recommend using this, since this is fairly obfuscated code with a lot of implicit functionality, but it's good to know nonetheless.