Formatting a number with exactly two decimals in JavaScript

StackOverflow https://stackoverflow.com/questions/1726630

Question

I have this line of code which rounds my numbers to two decimal places. But I get numbers like this: 10.8, 2.4, etc. These are not my idea of two decimal places so how I can improve the following?

Math.round(price*Math.pow(10,2))/Math.pow(10,2);

I want numbers like 10.80, 2.40, etc. Use of jQuery is fine with me.

Was it helpful?

Solution

To format a number using fixed-point notation, you can simply use the toFixed method:

(10.8).toFixed(2); // "10.80"

var num = 2.4;
alert(num.toFixed(2)); // "2.40"

Note that toFixed() returns a string.

IMPORTANT: Note that toFixed does not actually round, 90% of the time, it will return the rounded value but for many cases it doesn't actually work. Try this in your console:

2.005.toFixed(2)

You will get the wrong answer

There is no natural way of getting a decimal rounding in javascript, you will need your own polyfill or use a library. You can look at mozilla's polyfill for this https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/round

OTHER TIPS

This is an old topic but still top-ranked Google results and the solutions offered share the same floating point decimals issue. Here is the (very generic) function I use, thanks to MDN:

function round(value, exp) {
  if (typeof exp === 'undefined' || +exp === 0)
    return Math.round(value);

  value = +value;
  exp = +exp;

  if (isNaN(value) || !(typeof exp === 'number' && exp % 1 === 0))
    return NaN;

  // Shift
  value = value.toString().split('e');
  value = Math.round(+(value[0] + 'e' + (value[1] ? (+value[1] + exp) : exp)));

  // Shift back
  value = value.toString().split('e');
  return +(value[0] + 'e' + (value[1] ? (+value[1] - exp) : -exp));
}

As we can see, we don't get these issues:

round(1.275, 2);   // Returns 1.28
round(1.27499, 2); // Returns 1.27

This genericity also provides some cool stuff:

round(1234.5678, -2);   // Returns 1200
round(1.2345678e+2, 2); // Returns 123.46
round("123.45");        // Returns 123

Now, to answer the OP's question, one has to type:

round(10.8034, 2).toFixed(2); // Returns "10.80"
round(10.8, 2).toFixed(2);    // Returns "10.80"

Or, for a more concise, less generic function:

function round2Fixed(value) {
  value = +value;

  if (isNaN(value))
    return NaN;

  // Shift
  value = value.toString().split('e');
  value = Math.round(+(value[0] + 'e' + (value[1] ? (+value[1] + 2) : 2)));

  // Shift back
  value = value.toString().split('e');
  return (+(value[0] + 'e' + (value[1] ? (+value[1] - 2) : -2))).toFixed(2);
}

You can call it with:

round2Fixed(10.8034); // Returns "10.80"
round2Fixed(10.8);    // Returns "10.80"

Various examples and tests (thanks to @t-j-crowder!):

function round(value, exp) {
  if (typeof exp === 'undefined' || +exp === 0)
    return Math.round(value);

  value = +value;
  exp = +exp;

  if (isNaN(value) || !(typeof exp === 'number' && exp % 1 === 0))
    return NaN;

  // Shift
  value = value.toString().split('e');
  value = Math.round(+(value[0] + 'e' + (value[1] ? (+value[1] + exp) : exp)));

  // Shift back
  value = value.toString().split('e');
  return +(value[0] + 'e' + (value[1] ? (+value[1] - exp) : -exp));
}
function naive(value, exp) {
  if (!exp) {
    return Math.round(value);
  }
  var pow = Math.pow(10, exp);
  return Math.round(value * pow) / pow;
}
function test(val, places) {
  subtest(val, places);
  val = typeof val === "string" ? "-" + val : -val;
  subtest(val, places);
}
function subtest(val, places) {
  var placesOrZero = places || 0;
  var naiveResult = naive(val, places);
  var roundResult = round(val, places);
  if (placesOrZero >= 0) {
    naiveResult = naiveResult.toFixed(placesOrZero);
    roundResult = roundResult.toFixed(placesOrZero);
  } else {
    naiveResult = naiveResult.toString();
    roundResult = roundResult.toString();
  }
  $("<tr>")
    .append($("<td>").text(JSON.stringify(val)))
    .append($("<td>").text(placesOrZero))
    .append($("<td>").text(naiveResult))
    .append($("<td>").text(roundResult))
    .appendTo("#results");
}
test(0.565, 2);
test(0.575, 2);
test(0.585, 2);
test(1.275, 2);
test(1.27499, 2);
test(1234.5678, -2);
test(1.2345678e+2, 2);
test("123.45");
test(10.8034, 2);
test(10.8, 2);
test(1.005, 2);
test(1.0005, 2);
table {
  border-collapse: collapse;
}
table, td, th {
  border: 1px solid #ddd;
}
td, th {
  padding: 4px;
}
th {
  font-weight: normal;
  font-family: sans-serif;
}
td {
  font-family: monospace;
}
<table>
  <thead>
    <tr>
      <th>Input</th>
      <th>Places</th>
      <th>Naive</th>
      <th>Thorough</th>
    </tr>
  </thead>
  <tbody id="results">
  </tbody>
</table>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

I usually add this to my personal library, and after some suggestions and using the @TIMINeutron solution too, and making it adaptable for decimal length then, this one fits best: 

function precise_round(num, decimals) {
   var t = Math.pow(10, decimals);   
   return (Math.round((num * t) + (decimals>0?1:0)*(Math.sign(num) * (10 / Math.pow(100, decimals)))) / t).toFixed(decimals);
}

will work for the exceptions reported.

I don't know why can't I add a comment to a previous answer (maybe I'm hopelessly blind, dunno), but I came up with a solution using @Miguel's answer:

function precise_round(num,decimals) {
   return Math.round(num*Math.pow(10, decimals)) / Math.pow(10, decimals);
}

And its two comments (from @bighostkim and @Imre):

  • Problem with precise_round(1.275,2) not returning 1.28
  • Problem with precise_round(6,2) not returning 6.00 (as he wanted).

My final solution is as follows:

function precise_round(num,decimals) {
    var sign = num >= 0 ? 1 : -1;
    return (Math.round((num*Math.pow(10,decimals)) + (sign*0.001)) / Math.pow(10,decimals)).toFixed(decimals);
}

As you can see I had to add a little bit of "correction" (it's not what it is, but since Math.round is lossy - you can check it on jsfiddle.net - this is the only way I knew how to "fix" it). It adds 0.001 to the already padded number, so it is adding a 1 three 0s to the right of the decimal value. So it should be safe to use.

After that I added .toFixed(decimal) to always output the number in the correct format (with the right amount of decimals).

So that's pretty much it. Use it well ;)

EDIT: added functionality to the "correction" of negative numbers.

One way to be 100% sure that you get a number with 2 decimals: 

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

If this causes rounding errors, you can use the following as James has explained in his comment:

(Math.round((num * 1000)/10)/100).toFixed(2)

toFixed(n) provides n length after the decimal point; toPrecision(x) provides x total length.

Use this method below

// Example: toPrecision(4) when the number has 7 digits (3 before, 4 after)
    // It will round to the tenths place
    num = 500.2349;
    result = num.toPrecision(4); // result will equal 500.2

AND if you want the number to be fixed use

result = num.toFixed(2);

I didn't find an accurate solution for this problem, so I created my own:

function inprecise_round(value, decPlaces) {
  return Math.round(value*Math.pow(10,decPlaces))/Math.pow(10,decPlaces);
}

function precise_round(value, decPlaces){
    var val = value * Math.pow(10, decPlaces);
    var fraction = (Math.round((val-parseInt(val))*10)/10);

    //this line is for consistency with .NET Decimal.Round behavior
    // -342.055 => -342.06
    if(fraction == -0.5) fraction = -0.6;

    val = Math.round(parseInt(val) + fraction) / Math.pow(10, decPlaces);
    return val;
}

Examples:

function inprecise_round(value, decPlaces) {
  return Math.round(value * Math.pow(10, decPlaces)) / Math.pow(10, decPlaces);
}

function precise_round(value, decPlaces) {
  var val = value * Math.pow(10, decPlaces);
  var fraction = (Math.round((val - parseInt(val)) * 10) / 10);

  //this line is for consistency with .NET Decimal.Round behavior
  // -342.055 => -342.06
  if (fraction == -0.5) fraction = -0.6;

  val = Math.round(parseInt(val) + fraction) / Math.pow(10, decPlaces);
  return val;
}

// This may produce different results depending on the browser environment
console.log("342.055.toFixed(2)         :", 342.055.toFixed(2)); // 342.06 on Chrome & IE10

console.log("inprecise_round(342.055, 2):", inprecise_round(342.055, 2)); // 342.05
console.log("precise_round(342.055, 2)  :", precise_round(342.055, 2));   // 342.06
console.log("precise_round(-342.055, 2) :", precise_round(-342.055, 2));  // -342.06

console.log("inprecise_round(0.565, 2)  :", inprecise_round(0.565, 2));   // 0.56
console.log("precise_round(0.565, 2)    :", precise_round(0.565, 2));     // 0.57

@heridev and I created a small function in jQuery.

You can try next:

HTML

<input type="text" name="one" class="two-digits"><br>
<input type="text" name="two" class="two-digits">​

jQuery

// apply the two-digits behaviour to elements with 'two-digits' as their class
$( function() {
    $('.two-digits').keyup(function(){
        if($(this).val().indexOf('.')!=-1){         
            if($(this).val().split(".")[1].length > 2){                
                if( isNaN( parseFloat( this.value ) ) ) return;
                this.value = parseFloat(this.value).toFixed(2);
            }  
         }            
         return this; //for chaining
    });
});

​ DEMO ONLINE:

http://jsfiddle.net/c4Wqn/

Here's a simple one

function roundFloat(num,dec){
    var d = 1;
    for (var i=0; i<dec; i++){
        d += "0";
    }
    return Math.round(num * d) / d;
}

Use like alert(roundFloat(1.79209243929,4));

Jsfiddle

The trouble with floating point values is that they are trying to represent an infinite amount of (continuous) values with a fixed amount of bits. So naturally, there must be some loss in play, and you're going to be bitten with some values.

When a computer stores 1.275 as a floating point value, it won't actually remember whether it was 1.275 or 1.27499999999999993, or even 1.27500000000000002. These values should give different results after rounding to two decimals, but they won't, since for computer they look exactly the same after storing as floating point values, and there's no way to restore the lost data. Any further calculations will only accumulate such imprecision.

So, if precision matters, you have to avoid floating point values from the start. The simplest options are to

  • use a devoted library
  • use strings for storing and passing around the values (accompanied by string operations)
  • use integers (e.g. you could be passing around the amount of hundredths of your actual value, e.g. amount in cents instead of amount in dollars)

For example, when using integers to store the number of hundredths, the function for finding the actual value is quite simple:

function descale(num, decimals) {
    var hasMinus = num < 0;
    var numString = Math.abs(num).toString();
    var precedingZeroes = '';
    for (var i = numString.length; i <= decimals; i++) {
        precedingZeroes += '0';
    }
    numString = precedingZeroes + numString;
    return (hasMinus ? '-' : '') 
        + numString.substr(0, numString.length-decimals) 
        + '.' 
        + numString.substr(numString.length-decimals);
}

alert(descale(127, 2));

With strings, you'll need rounding, but it's still manageable:

function precise_round(num, decimals) {
    var parts = num.split('.');
    var hasMinus = parts.length > 0 && parts[0].length > 0 && parts[0].charAt(0) == '-';
    var integralPart = parts.length == 0 ? '0' : (hasMinus ? parts[0].substr(1) : parts[0]);
    var decimalPart = parts.length > 1 ? parts[1] : '';
    if (decimalPart.length > decimals) {
        var roundOffNumber = decimalPart.charAt(decimals);
        decimalPart = decimalPart.substr(0, decimals);
        if ('56789'.indexOf(roundOffNumber) > -1) {
            var numbers = integralPart + decimalPart;
            var i = numbers.length;
            var trailingZeroes = '';
            var justOneAndTrailingZeroes = true;
            do {
                i--;
                var roundedNumber = '1234567890'.charAt(parseInt(numbers.charAt(i)));
                if (roundedNumber === '0') {
                    trailingZeroes += '0';
                } else {
                    numbers = numbers.substr(0, i) + roundedNumber + trailingZeroes;
                    justOneAndTrailingZeroes = false;
                    break;
                }
            } while (i > 0);
            if (justOneAndTrailingZeroes) {
                numbers = '1' + trailingZeroes;
            }
            integralPart = numbers.substr(0, numbers.length - decimals);
            decimalPart = numbers.substr(numbers.length - decimals);
        }
    } else {
        for (var i = decimalPart.length; i < decimals; i++) {
            decimalPart += '0';
        }
    }
    return (hasMinus ? '-' : '') + integralPart + (decimals > 0 ? '.' + decimalPart : '');
}

alert(precise_round('1.275', 2));
alert(precise_round('1.27499999999999993', 2));

Note that this function rounds to nearest, ties away from zero, while IEEE 754 recommends rounding to nearest, ties to even as the default behavior for floating point operations. Such modifications are left as an exercise for the reader :)

Round your decimal value, then use toFixed(x) for your expected digit(s).

function parseDecimalRoundAndFixed(num,dec){
  var d =  Math.pow(10,dec);
  return (Math.round(num * d) / d).toFixed(dec);
}

Call

parseDecimalRoundAndFixed(10.800243929,4) => 10.80 parseDecimalRoundAndFixed(10.807243929,2) => 10.81

/**
 * MidpointRounding away from zero ('arithmetic' rounding)
 * Uses a half-epsilon for correction. (This offsets IEEE-754
 * half-to-even rounding that was applied at the edge cases).
 */

function RoundCorrect(num, precision = 2) {
	// half epsilon to correct edge cases.
	var c = 0.5 * Number.EPSILON * num;
//	var p = Math.pow(10, precision); //slow
	var p = 1; while (precision--> 0) p *= 10;
	if (num < 0)
		p *= -1;
	return Math.round((num + c) * p) / p;
}

// testing some +ve edge cases
console.log(RoundCorrect(1.005, 2));  // 1.01 correct
console.log(RoundCorrect(2.175, 2));  // 2.18 correct
console.log(RoundCorrect(5.015, 2));  // 5.02 correct

// testing some -ve edge cases
console.log(RoundCorrect(-1.005, 2));  // -1.01 correct
console.log(RoundCorrect(-2.175, 2));  // -2.18 correct
console.log(RoundCorrect(-5.015, 2));  // -5.02 correct

Here is my 1-line solution: Number((yourNumericValueHere).toFixed(2));

Here's what happens:

1) First, you apply .toFixed(2) onto the number that you want to round off the decimal places of. Note that this will convert the value to a string from number. So if you are using Typescript, it will throw an error like this:

"Type 'string' is not assignable to type 'number'"

2) To get back the numeric value or to convert the string to numeric value, simply apply the Number() function on that so-called 'string' value.

For clarification, look at the example below:

EXAMPLE: I have an amount that has upto 5 digits in the decimal places and I would like to shorten it to upto 2 decimal places. I do it like so:

var price = 0.26453;
var priceRounded = Number((price).toFixed(2));
console.log('Original Price: ' + price);
console.log('Price Rounded: ' + priceRounded);

Put the following in some global scope:

Number.prototype.getDecimals = function ( decDigCount ) {
   return this.toFixed(decDigCount);
}

and then try:

var a = 56.23232323;
a.getDecimals(2); // will return 56.23

Update

Note that toFixed() can only work for the number of decimals between 0-20 i.e. a.getDecimals(25) may generate a javascript error, so to accomodate that you may add some additional check i.e.

Number.prototype.getDecimals = function ( decDigCount ) {
   return ( decDigCount > 20 ) ? this : this.toFixed(decDigCount);
}

Number(((Math.random() * 100) + 1).toFixed(2))

this will return a random number from 1 to 100 rounded to 2 decimal places.

Number(Math.round(1.005+'e2')+'e-2'); // 1.01

This worked for me: Rounding Decimals in JavaScript

Using this response by reference: https://stackoverflow.com/a/21029698/454827

I build a function to get dynamic numbers of decimals:

function toDec(num, dec)
{
        if(typeof dec=='undefined' || dec<0)
                dec = 2;

        var tmp = dec + 1;
        for(var i=1; i<=tmp; i++)
                num = num * 10;

        num = num / 10;
        num = Math.round(num);
        for(var i=1; i<=dec; i++)
                num = num / 10;

        num = num.toFixed(dec);

        return num;
}

here working example: https://jsfiddle.net/wpxLduLc/

parse = function (data) {
       data = Math.round(data*Math.pow(10,2))/Math.pow(10,2);
       if (data != null) {
            var lastone = data.toString().split('').pop();
            if (lastone != '.') {
                 data = parseFloat(data);
            }
       }
       return data;
  };

$('#result').html(parse(200)); // output 200
$('#result1').html(parse(200.1)); // output 200.1
$('#result2').html(parse(200.10)); // output 200.1
$('#result3').html(parse(200.109)); // output 200.11
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.0.0/jquery.min.js"></script>
<div id="result"></div>
<div id="result1"></div>
<div id="result2"></div>
<div id="result3"></div>

Round down

function round_down(value, decPlaces) {
    return Math.floor(value * Math.pow(10, decPlaces)) / Math.pow(10, decPlaces);
}

Round up

function round_up(value, decPlaces) {
    return Math.ceil(value * Math.pow(10, decPlaces)) / Math.pow(10, decPlaces);
}

Round nearest

function round_nearest(value, decPlaces) {
    return Math.round(value * Math.pow(10, decPlaces)) / Math.pow(10, decPlaces);
}

Merged https://stackoverflow.com/a/7641824/1889449 and https://www.kirupa.com/html5/rounding_numbers_in_javascript.htm Thanks them.

With these examples you will still get an error when trying to round the number 1.005 the solution is to either use a library like Math.js or this function:

function round(value: number, decimals: number) {
    return Number(Math.round(value + 'e' + decimals) + 'e-' + decimals);
}

I got some ideas from this post a few months back, but none of the answers here, nor answers from other posts/blogs could handle all the scenarios (e.g. negative numbers and some "lucky numbers" our tester found). In the end, our tester did not find any problem with this method below. Pasting a snippet of my code:

fixPrecision: function (value) {
    var me = this,
        nan = isNaN(value),
        precision = me.decimalPrecision;

    if (nan || !value) {
        return nan ? '' : value;
    } else if (!me.allowDecimals || precision <= 0) {
        precision = 0;
    }

    //[1]
    //return parseFloat(Ext.Number.toFixed(parseFloat(value), precision));
    precision = precision || 0;
    var negMultiplier = value < 0 ? -1 : 1;

    //[2]
    var numWithExp = parseFloat(value + "e" + precision);
    var roundedNum = parseFloat(Math.round(Math.abs(numWithExp)) + 'e-' + precision) * negMultiplier;
    return parseFloat(roundedNum.toFixed(precision));
},

I also have code comments (sorry i forgot all the details already)...I'm posting my answer here for future reference:

9.995 * 100 = 999.4999999999999
Whereas 9.995e2 = 999.5
This discrepancy causes Math.round(9.995 * 100) = 999 instead of 1000.
Use e notation instead of multiplying /dividing by Math.Pow(10,precision).

I'm fix the problem the modifier. Support 2 decimal only.

$(function(){
  //input number only.
  convertNumberFloatZero(22); // output : 22.00
  convertNumberFloatZero(22.5); // output : 22.50
  convertNumberFloatZero(22.55); // output : 22.55
  convertNumberFloatZero(22.556); // output : 22.56
  convertNumberFloatZero(22.555); // output : 22.55
  convertNumberFloatZero(22.5541); // output : 22.54
  convertNumberFloatZero(22222.5541); // output : 22,222.54

  function convertNumberFloatZero(number){
	if(!$.isNumeric(number)){
		return 'NaN';
	}
	var numberFloat = number.toFixed(3);
	var splitNumber = numberFloat.split(".");
	var cNumberFloat = number.toFixed(2);
	var cNsplitNumber = cNumberFloat.split(".");
	var lastChar = splitNumber[1].substr(splitNumber[1].length - 1);
	if(lastChar > 0 && lastChar < 5){
		cNsplitNumber[1]--;
	}
	return Number(splitNumber[0]).toLocaleString('en').concat('.').concat(cNsplitNumber[1]);
  };
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>

(Math.round((10.2)*100)/100).toFixed(2)

That should yield: 10.20

(Math.round((.05)*100)/100).toFixed(2)

That should yield: 0.05

(Math.round((4.04)*100)/100).toFixed(2)

That should yield: 4.04

etc.

/*Due to all told stuff. You may do 2 things for different purposes:
When showing/printing stuff use this in your alert/innerHtml= contents:
YourRebelNumber.toFixed(2)*/

var aNumber=9242.16;
var YourRebelNumber=aNumber-9000;
alert(YourRebelNumber);
alert(YourRebelNumber.toFixed(2));

/*and when comparing use:
Number(YourRebelNumber.toFixed(2))*/

if(YourRebelNumber==242.16)alert("Not Rounded");
if(Number(YourRebelNumber.toFixed(2))==242.16)alert("Rounded");

/*Number will behave as you want in that moment. After that, it'll return to its defiance.
*/

This is very simple and works just as well as any of the others:

function parseNumber(val, decimalPlaces) {
    if (decimalPlaces == null) decimalPlaces = 0
    var ret = Number(val).toFixed(decimalPlaces)
    return Number(ret)
}

Since toFixed() can only be called on numbers, and unfortunately returns a string, this does all the parsing for you in both directions. You can pass a string or a number, and you get a number back every time! Calling parseNumber(1.49) will give you 1, and parseNumber(1.49,2) will give you 1.50. Just like the best of 'em!

You could also use the .toPrecision() method and some custom code, and always round up to the nth decimal digit regardless the length of int part.

function glbfrmt (number, decimals, seperator) {
    return typeof number !== 'number' ? number : number.toPrecision( number.toString().split(seperator)[0].length + decimals);
}

You could also make it a plugin for a better use.

Simple as this.

var rounded_value=Math.round(value * 100) / 100;

I found a very simple way that solved this problem for me and can be used or adapted:

td[row].innerHTML = price.toPrecision(price.toFixed(decimals).length

100% working!!! Try it

<html>
     <head>
      <script>
      function replacePonto(){
        var input = document.getElementById('qtd');
        var ponto = input.value.split('.').length;
        var slash = input.value.split('-').length;
        if (ponto > 2)
                input.value=input.value.substr(0,(input.value.length)-1);

        if(slash > 2)
                input.value=input.value.substr(0,(input.value.length)-1);

        input.value=input.value.replace(/[^0-9.-]/,'');

        if (ponto ==2)
	input.value=input.value.substr(0,(input.value.indexOf('.')+3));

if(input.value == '.')
	input.value = "";
              }
      </script>
      </head>
      <body>
         <input type="text" id="qtd" maxlength="10" style="width:140px" onkeyup="return replacePonto()">
      </body>
    </html>

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