Javascript Rounding issues

Question

I tried using this:

//var value = "39.99";
//var value = "0.255";
var list = ["39.99", "0.255", "0.306", "0.645", "2.505", "5.726", "9.649", "9.999", "10.01", "0.155", "0.355", "10.05", "14.75", "14.02", "2.405", "14.54","2.485"];


var result;

for( i in list ){
    //result = processRounding(parseFloat(list[i]).toFixed(3));
    //result = parseFloat(list[i]).toFixed(2);
    result = test(parseFloat(list[i]).toFixed(3), 2);
    console.log("RESULT["+i+"]: "+ format("#,##0.00", result));
}

function test(value, precision) {
    var precision = precision || 0,
    neg = value < 0,
    power = Math.pow(10, precision),
    value = Math.round(value * power),
    integral = String((neg ? Math.ceil : Math.floor)(value / power)),
    fraction = String((neg ? -value : value) % power),
    padding = new Array(Math.max(precision - fraction.length, 0) + 1).join('0');

    return precision ? integral + '.' +  padding + fraction : integral;
}


function processRounding (value){
    //console.log( Math.ceil(value*100) + " " +  Math.ceil(value*100) / 2);
    var remainder = parseFloat(value % 1).toFixed(2);
    var floor     = parseInt(Math.floor(value));
    console.log(floor + " " + remainder);
    if(Math.floor(value) != 0 && Math.floor(value) > 10){
        if( parseFloat(remainder) > 0.50 || parseFloat(remainder) > 0.05 ){
            console.log("CEIL");
            value = Math.ceil(value*10)/10;
        }else{
            value = value;
        }          
    }else{
        if( parseFloat(remainder) > 0.50 || parseFloat(remainder) > 0.05 ){
            console.log("ROUND");
            value = Math.round(value*100)/100;
        }else{
            value = value;
        } 
    }

    return value;
}

[jsFiddle here]

But the problem I see is that when the value is something like "2.405" what it does is simple make it "2.40" regardless if I use either the function test or the function processRounding in my jsfiddle example.

Any Ideas on how to make the result into 2.41? Technically It should round up right since the last digit is "5".

UPDATE

using result = test(parseFloat(list[i]).toFixed(3), 2);

var list = ["39.99", "0.255", "0.306", "0.645", "2.505", "5.726", "9.649", "9.999", "10.01", "0.155", "0.355", "10.05", "14.75", "14.02", "2.405", "14.54","2.485"];

would result to this :

RESULT[0]: 39.99
RESULT[1]: 0.26 
RESULT[2]: 0.31 
RESULT[3]: 0.65 
RESULT[4]: 2.51 
RESULT[5]: 5.73 
RESULT[6]: 9.65 
RESULT[7]: 10.00 
RESULT[8]: 10.01 
RESULT[9]: 0.16 
RESULT[10]: 0.36
RESULT[11]: 10.05
RESULT[12]: 14.75
RESULT[13]: 14.02
RESULT[14]: 2.40
RESULT[15]: 14.54
RESULT[16]: 2.49

Notice that in the list there is a "2.405" value which in the result[14] it is "2.40" it should be in 2.41 right?

there's a lot going on in that fiddle. Can you post the relevant section here? — Ben McCormick, Mar 11 '13 at 02:09

score 3 · Answer 1 · edited May 23 '17 at 10:32

3

I think you wish to have a round off function in JavaScript.

function trueRound(value, digits){
    return (Math.round((value*Math.pow(10,digits)).toFixed(digits-1))/Math.pow(10,digits)).toFixed(digits);
}

Possibly duplicated question: round off decimal using javascript

edited May 23 '17 at 10:32

Community

1
1

answered Mar 11 '13 at 02:11

Roger Ng

771
11
28

okay it did work. but my question is how about the value 39.99 it should be rounded off to 40 right? – n0minal Mar 11 '13 at 02:19
To round a number to the nearest integer: `Math.round(x)` – Roger Ng Mar 11 '13 at 02:22
2

@Dreyfus15 It works that way for me testing it just now... trueRound(39.99,1) returns 40.0 – Ben McCormick Mar 11 '13 at 02:23
I'm using this trueRound(parseFloat(value).toFixed(2), 2) simply because 0.255 should be rounded off to 0.26 not 0.30 – n0minal Mar 11 '13 at 02:26

score 0 · Answer 2 · answered Mar 11 '13 at 02:13

0

You're starting off by cutting the remainder off to 2 decimals: parseFloat(value % 1).toFixed(2);

That means when you have 2.405 the remainder is parsed as .40 and it won't be able to differentiate between 2.400 and 2.409

You're going to want to keep the full remainder if you want to round that correctly.

Roger Ng has a good solution. I just wanted to explain why yours has no chance of working from the start.

answered Mar 11 '13 at 02:13

Ben McCormick

25,260
12
52
71

I also tried using toFixed(3) to be able to retrieve .405 yet same results. – n0minal Mar 11 '13 at 02:16

Javascript Rounding issues

2 Answers2