Need help to round up decimals Javascript

Question

Im trying to round up 2 number and adding them after.

var a = 12.24; var b = 12.27;

i want them to round up to 12.5 so when i add these 2 numbers the result will be 12.5 + 12.5 = 25

Answer 1

It's the same as shown in this answer, using a different multiplier/divisor. In that question, they wanted the nearest 10th; in this question, you want the nearest half. So instead of

var num = 12.24;
num = Math.ceil(num * 10) / 10;
alert(num); // 12.24

...we use

var num = 12.24;
num = Math.ceil(num * 2) / 2;
alert(num); // 12.5

Answer 2

To round to the nearest half, use

Math.round(a / 0.5) * 0.5;

To round up to the nearest half, use

Math.ceil(a / 0.5) * 0.5; But note two things:

1. Floating point arithmetic might still cause a fractionally-rounded number to be off. (But note that half-rounded numbers can be represented accurately in floating point to the 52nd power of 2).

2. You can achieve your result by summing the numbers then rounding the result. That will be more numerically stable.

Answer 3

You can try the following. Here is a Jsfiddle.

var a = 12.24;
console.log(roundHalf(a)); // 12.5
var b = 12.27;
console.log(roundHalf(b)); // 12.5
var result = roundHalf(a) + roundHalf(b);
console.log(result); // 25

function roundHalf(num){
    return Math.ceil(num * 2) / 2;
}