Negative zero in JavaScript?

Question

I've just noticed that I can do the following in JavaScript:

var z = -0;
console.log(z); // prints -0

Why does the unary negation works on zero?

Is this one of the many JavaScript quirks or it does (somehow) have a purpose?

P.S.:

It seems to be happening on Firefox 38.0a2 and Chrome 41.0.2272. On Node.js v0.10.36 doesn't happen. Dunno about IE.

Checkout this: http://stackoverflow.com/questions/7223359/are-0-and-0-the-same — Spencer May, Mar 23 '15 at 20:31

score 11 · Accepted Answer · answered Mar 23 '15 at 20:33

You've just encountered the signed zero.

The IEEE 754 standard for floating-point arithmetic (presently used by most computers and programming languages that support floating point numbers) requires both +0 and −0. Real arithmetic with signed zeros can be considered a variant of the extended real number line such that 1/−0 = −∞ and 1/+0 = +∞; division is only undefined for ±0/±0 and ±∞/±∞.

All numbers in Javascript are floating-point, so zeros must be signed.

score 0 · Answer 2 · answered Mar 23 '15 at 20:34

0

I think this is not a problem. At least alert(-0 == 0) returns true. I guess if there is one bit used for the sign this bit can also be set if the value is 0. Hovever, it remains the same number.

answered Mar 23 '15 at 20:34

bweber

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Negative zero in JavaScript?

2 Answers2