javascript - Why does Math.round(-0.2) return -0? - Stack Overflow

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I had a little problem with Javascript today:

I have a collection of values, for example:

US         11.3123
Brazil     -0.2291
UK          0.4501

I want to display with no decimal places, rounding values, so it will be displayed as:

US         11
Brazil     -0
UK          0

So, the problem is that Brazil is showing "-0" instead of "0".

Well, I can workaround easily:

html += '<tr><td>' + arr[i].Country + '</td>' +
            '<td>' + d3.format(arr[i].Value || 0, 0) + '</td></tr>';

Why does Math.round return -0 instead of 0?

Update

I'm using D3.js format function, which transmits JavaScript behavior to output. But still, I have this doubt due to the fact that in console:

Math.round(-0.02)
> -0

I had a little problem with Javascript today:

I have a collection of values, for example:

US         11.3123
Brazil     -0.2291
UK          0.4501

I want to display with no decimal places, rounding values, so it will be displayed as:

US         11
Brazil     -0
UK          0

So, the problem is that Brazil is showing "-0" instead of "0".

Well, I can workaround easily:

html += '<tr><td>' + arr[i].Country + '</td>' +
            '<td>' + d3.format(arr[i].Value || 0, 0) + '</td></tr>';

Why does Math.round return -0 instead of 0?

Update

I'm using D3.js format function, which transmits JavaScript behavior to output. But still, I have this doubt due to the fact that in console:

Math.round(-0.02)
> -0

• javascript

Share Improve this question Follow edited Mar 26, 2014 at 1:58 Andre Figueiredo asked Mar 26, 2014 at 1:16 Andre FigueiredoAndre Figueiredo 13.4k88 gold badges5151 silver badges7575 bronze badges 1

• 1 Detecting minus zero is possible by seeing which limit it goes to, for example, var x = -0; 1 / x === -Infinity; // true. If you want to get rid of it safely, adding a +0 to a -0 will give +0, or you can use x || 0 because -0 is falsy. – Paul S. Commented Mar 26, 2014 at 2:15

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 9

From the ecmascript definition: http://es5.github.io/#x15.8.2.15

If x is NaN, the result is NaN.
If x is +0, the result is +0.
If x is −0, the result is −0.
If x is +∞, the result is +∞.
If x is −∞, the result is −∞.
If x is greater than 0 but less than 0.5, the result is +0.
If x is less than 0 but greater than or equal to -0.5, the result is −0.

NOTE 2 The value of Math.round(x) is the same as the value of Math.floor(x+0.5), except when x is −0 or is less than 0 but greater than or equal to -0.5; for these cases Math.round(x) returns −0, but Math.floor(x+0.5) returns +0.

the problem is that Brazil is showing "-0" instead of "0".

It must not. While @JoeFrambach and @Amdan explained that and why JS does distinguish between +0 and -0, this must not be output from your code (unless your JS engine is flawed). To cite EcmaScript §9.8.1 ToString Applied to the Number Type:

2. If [the number] is +0 or −0, return the String "0"

No minus sign:

Math.round(-0.2) + '' == "0"
Math.round( 0.2) + '' == "0"

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