Differentiating +0 and -0

This is still some kind of hack, but a look at the specs suggests this:

Math.atan2(0, -0) === Math.PI // true
Math.atan2(0,  0) === 0       // true

In ECMAScript 6 Object.is behaves like === except that it distinguishes positive and negative zeroes, and Object.is(NaN, NaN) evaluates to true. (See here for a writeup.)

Chrome 24 supports Object.is.