Javascript VS PHP rounding

Question

I am having some problems with the way PHP and javascript round numbers. I am using PHP's round function and this javascript function:

function roundNumber(number, decimals) {     
    var newnumber = new Number(number+'').toFixed(parseInt(decimals));
    var value = parseFloat(newnumber);
    return value;
}

The number i am trying to round is 43.65 * 2.5 + 40% which when done using a calculator = 152.775 or when rounded in PHP = 152.78.

In javascript when i do a console.log the number is 152.774999999998 and when rounded with the above function gives me 152.77

Any help to reslove this issue is greatly appreciated

This is why we do not use floating-point numbers for currency. — Ignacio Vazquez-Abrams, Jun 22 '11 at 08:37
http://stackoverflow.com/questions/5490687/broken-tofixed-implementation — mplungjan, Jun 22 '11 at 08:39
Make sure when you use `parseInt` that you specify a radix; usually you want to work in base 10, so: `parseInt(yourNumber,10)`. — nnnnnn, Jun 22 '11 at 08:46
Can someone explain to me why in PHP round(22.044960000000003,2) becomes 22.04 And round( 152.77499999999998,2) becomes 152.78 Why is the second one rounding up to 152.78 when i only want 2 dp's — Pjn2020, Jun 22 '11 at 12:33

score 5 · Answer 1 · answered Jun 22 '11 at 08:37

5

This isn't anything to do with rounding per se, but is to do with how decimal numbers are represented in binary-based hardware.

Check out the floating point guide for lots more information on this, as well as solutions/alternatives.

answered Jun 22 '11 at 08:37

Andrzej Doyle

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score 4 · Accepted Answer · edited May 23 '17 at 10:27

Please have a look at How to deal with floating point number precision in JavaScript?

Here is an example

function roundNumber(number, decimals) {
  decimals = parseInt(decimals,10);
  var dec = Math.pow(10,decimals)
  console.log(dec,parseFloat(number)*dec);
  number=""+Math.round(parseFloat(number)*dec+.0000000000001); // fixed the .X99999999999
  return parseFloat(number.slice(0,-1*decimals) + "." + number.slice(-1*decimals))     
}


var val = 43.65 * 2.5;
    val+= val*0.40

console.log(val+' ~= 152.78? --> '+roundNumber(val,2).toFixed(2));
console.log('15.803 ~= 15.80? --> '+roundNumber(15.803,2).toFixed(2));
console.log('15.805 ~= 15.81? --> '+roundNumber(15.805,2).toFixed(2));
console.log('14.803 ~= 14.80? --> '+roundNumber(14.803,2).toFixed(2));
console.log('0.575 ~=  0.58? --> '+roundNumber(0.575,2).toFixed(2));

fails with 15.803, gives 15.81 while it should give 15.80 – max4ever Oct 04 '11 at 11:06 — max4ever, Oct 04 '11 at 11:06
Works for 25.575 (=> 25.58) but fails for 0.575 (=> 0.57) – modernzombie May 16 '14 at 19:08 — modernzombie, May 16 '14 at 19:08

aorcsik · Answer 3 · 2011-06-22T11:29:40.130

3

I was thinking a bit on this, and wanted to share my solution, let it not go to waste:

function roundNumber(number, decimals) {      
    var d = parseInt(decimals,10),
        dx = Math.pow(10,d),
        n = parseFloat(number),
        f = Math.round(Math.round(n * dx * 10) / 10) / dx;
    return f.toFixed(d);
}

This does not use string functions, or any forced up or down rounding.

Test it here: http://jsfiddle.net/inti/hMrsp/4/

Edit: corrected, was cutting down zeros at the end

edited Jun 22 '11 at 11:29

answered Jun 22 '11 at 10:19

aorcsik

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Fails on var v = 152.79499999999998; - loses the trailing 0 – mplungjan Jun 22 '11 at 11:23
thanks dude, for some reason this one works with everything while mplungjan's version fails on 14.803 for example – max4ever Oct 04 '11 at 11:06

score 1 · Answer 4 · answered Jun 22 '11 at 08:38

1

php rounds to 152.78, because it sees 152.77499 which is 152.775 and in the end 152.178. can't you use rounded value from php?

answered Jun 22 '11 at 08:38

Dimitar Marinov

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score 1 · Answer 5 · answered Jun 22 '11 at 08:59

1

It is because the different precisions used in JS (by the browser) and PHP or actually how many bits are used to store the numbers.

you can make your JS rounding function do this to round to the 2nd digit Math.round(floatNumber*100)/100

answered Jun 22 '11 at 08:59

venimus

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score -1 · Answer 6 · answered Jun 22 '11 at 08:41

Find below javascript function for number format

<script type="text/javascript">
function format_number(pnumber,decimals){
    if (isNaN(pnumber)) { return 0};
    if (pnumber=='') { return 0};

    var snum = new String(pnumber);
    var sec = snum.split('.');
    var whole = parseFloat(sec[0]);
    var result = '';

    if(sec.length > 1){
        var dec = new String(sec[1]);
        dec = String(parseFloat(sec[1])/Math.pow(10,(dec.length - decimals)));
        dec = String(whole + Math.round(parseFloat(dec))/Math.pow(10,decimals));
        var dot = dec.indexOf('.');
        if(dot == -1){
            dec += '.';
            dot = dec.indexOf('.');
        }
        while(dec.length <= dot + decimals) { dec += '0'; }
        result = dec;
    } else{
        var dot;
        var dec = new String(whole);
        dec += '.';
        dot = dec.indexOf('.');
        while(dec.length <= dot + decimals) { dec += '0'; }
        result = dec;
    }   
    return result;
}

var value = format_number(newnumber,2);
</script>

That seems a bit excessive - and I find it poor form not to credit where you got it from. http://www.codingforums.com/archive/index.php/t-190997.html — mplungjan, Jun 22 '11 at 08:54

Javascript VS PHP rounding

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