javascript - Round negative value to 2 decimal places - Stack Overflow

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I have two negative value -0.245 and -9.085. I want make them to 2 decimal places. I am using JavaScript function toFixed() but getting some weird result.

Please help me to under stand the logic behind the first example being rounded "down" but the second being rounded "up"

//Examples 1. result ing as expected
var num = -0.245
var n = num.toFixed(2); //-0.24
console.log(n);

//Examples 2. result should be -9.08
num = -9.085
n = num.toFixed(2); //-9.09
console.log(n);

I have two negative value -0.245 and -9.085. I want make them to 2 decimal places. I am using JavaScript function toFixed() but getting some weird result.

Please help me to under stand the logic behind the first example being rounded "down" but the second being rounded "up"

//Examples 1. result ing as expected
var num = -0.245
var n = num.toFixed(2); //-0.24
console.log(n);

//Examples 2. result should be -9.08
num = -9.085
n = num.toFixed(2); //-9.09
console.log(n);

• javascript
• math
• decimal

Share Improve this question Follow edited Sep 29, 2016 at 11:10 mplungjan 178k2828 gold badges181181 silver badges240240 bronze badges asked Sep 29, 2016 at 11:03 Rakesh KumarRakesh Kumar 2,85511 gold badge2222 silver badges3636 bronze badges 3

• what result you are getting? – Mirza Obaid Commented Sep 29, 2016 at 11:09
• Example 1 answer (-0.24) is the answer I want and according to that example 2 answer should be -9.08 instead -9.09. – Rakesh Kumar Commented Sep 29, 2016 at 11:09
• Is floating point math broken? might be relevant here. – 001 Commented Sep 29, 2016 at 11:18

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5 Answers 5

Sorted by: Reset to default 5

as per description in https://developer.mozilla/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toFixed mention:

The number is rounded if necessary, and the fractional part is padded with zeros if necessary so that it has the specified length.

For -0.245.toFixed(2), the value is negative and the value after 2 decimal places is -0.045, -0.045 is higher than -0.05, so the result is rounded up to -0.24

For -9.085.toFixed(2), the value is negative and the value after 2 decimal places is -0.085, -0.085 is lower than -0.08, so the result is rounded down to -9.09

Below is solution to always round up to 2 decimal places for negative value.

var num = -9.085
var output = num < 0 ? Math.floor(Math.abs(num) * 100) * -1 / 100 : num.toFixed(2)
console.log(output) //-9.08

toFixed() returns a string representation of numObj that does not use exponential notation and has exactly digits digits after the decimal place. The number is rounded if necessary, and the fractional part is padded with zeros if necessary so that it has the specified length.

Which means the result is not wrong but you expecting toFixed() to do something diffrent. If you round -9.085 to second decimal place the mathematic correct result is -9.09 (.5 round up the next decimal). What you are trying to acplish is to remove everything after the second decimal which can be acplished with:

parseInt(-9.085 * 100) / 100 //-9.08

alert(parseInt(-9.085 * 100) / 100)

Please check, this helps you alot in understanding the logic behind this: https://developer.mozilla/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toFixed

This function rounds off the values. E.g. if the value is between 9.080 to 9.084 the result would be 9.08 and if the value is 9.085 to 9.089 the result would be 9.09.

  parseFloat(Math.round(num * 100) / 100).toFixed(2);

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