CODEWITHSUNDEEP
javascriptroundingdecimal-point
Abs
Abs

Reputation: 57916

Formatting a number with exactly two decimals in JavaScript

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.

Upvotes: 654

Views: 979570

Answers (30)

Maruf Alam
Maruf Alam

Reputation: 598

fun Any.twoDecimalPlaces(numInDouble: Double): String {

    return "%.2f".format(numInDouble)
}

Upvotes: 0

H. Almidan
H. Almidan

Reputation: 518

Building on top of Christian C. Salvadó's answer, doing the following will output a Number type, and also seems to be dealing with rounding well:

const roundNumberToTwoDecimalPlaces = (num) => Number(new Intl.NumberFormat('en-US', {
  minimumFractionDigits: 2,
  maximumFractionDigits: 2,
}).format(num));

roundNumberToTwoDecimalPlaces(1.344); // => 1.34
roundNumberToTwoDecimalPlaces(1.345); // => 1.35

The difference between the above and what has already been mentioned is that you don't need the .format() chaining when you're using it[, and that it outputs a Number type].

Upvotes: 4

tfrascaroli
tfrascaroli

Reputation: 1219

I don't know why can't I add a comment to a previous answer (maybe I'm hopelessly blind, I don't know), 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.

Upvotes: 18

user15102407
user15102407

Reputation: 257

FAST AND EASY

parseFloat(number.toFixed(2))

Example

let number = 2.55435930

let roundedString = number.toFixed(2)    // "2.55"

let twoDecimalsNumber = parseFloat(roundedString)    // 2.55

let directly = parseFloat(number.toFixed(2))    // 2.55

Upvotes: 24

Amr Ali
Amr Ali

Reputation: 3698

In general, decimal rounding is done by scaling: round(num * p) / p

Naive implementation

Using the following function with halfway numbers, you will get either the upper rounded value as expected, or the lower rounded value sometimes depending on the input.

This inconsistency in rounding may introduce hard to detect bugs in the client code.

function naiveRound(num, decimalPlaces) {
    var p = Math.pow(10, decimalPlaces);
    return Math.round(num * p) / p;
}

console.log( naiveRound(1.245, 2) );  // 1.25 correct (rounded as expected)
console.log( naiveRound(1.255, 2) );  // 1.25 incorrect (should be 1.26)

Better implementations

By converting the number to a string in the exponential notation, positive numbers are rounded as expected. But, be aware that negative numbers round differently than positive numbers.

In fact, it performs what is basically equivalent to "round half up" as the rule, you will see that round(-1.005, 2) evaluates to -1 even though round(1.005, 2) evaluates to 1.01. The lodash _.round method uses this technique.

/**
 * Round half up ('round half towards positive infinity')
 * Uses exponential notation to avoid floating-point issues.
 * Negative numbers round differently than positive numbers.
 */
function round(num, decimalPlaces) {
    num = Math.round(num + "e" + decimalPlaces);
    return Number(num + "e" + -decimalPlaces);
}

// test rounding of half
console.log( round(0.5, 0) );  // 1
console.log( round(-0.5, 0) ); // 0

// testing edge cases
console.log( round(1.005, 2) );   // 1.01
console.log( round(2.175, 2) );   // 2.18
console.log( round(5.015, 2) );   // 5.02

console.log( round(-1.005, 2) );  // -1
console.log( round(-2.175, 2) );  // -2.17
console.log( round(-5.015, 2) );  // -5.01

If you want the usual behavior when rounding negative numbers, you would need to convert negative numbers to positive before calling Math.round(), and then convert them back to negative numbers before returning.

// Round half away from zero
function round(num, decimalPlaces) {
    num = Math.round(Math.abs(num) + "e" + decimalPlaces) * Math.sign(num);
    return Number(num + "e" + -decimalPlaces);
}

There is a different purely mathematical technique to perform round-to-nearest (using "round half away from zero"), in which epsilon correction is applied before calling the rounding function.

Simply, we add the smallest possible float value (= 1.0 ulp; unit in the last place) to the number before rounding. This moves to the next representable value after the number, away from zero.

/**
 * Round half away from zero ('commercial' rounding)
 * Uses correction to offset floating-point inaccuracies.
 * Works symmetrically for positive and negative numbers.
 */
function round(num, decimalPlaces) {
    var p = Math.pow(10, decimalPlaces);
    var e = Number.EPSILON * num * p;
    return Math.round((num * p) + e) / p;
}

// test rounding of half
console.log( round(0.5, 0) );  // 1
console.log( round(-0.5, 0) ); // -1

// testing edge cases
console.log( round(1.005, 2) );  // 1.01
console.log( round(2.175, 2) );  // 2.18
console.log( round(5.015, 2) );  // 5.02

console.log( round(-1.005, 2) ); // -1.01
console.log( round(-2.175, 2) ); // -2.18
console.log( round(-5.015, 2) ); // -5.02

This is needed to offset the implicit round-off error that may occur during encoding of decimal numbers, particularly those having "5" in the last decimal position, like 1.005, 2.675 and 16.235. Actually, 1.005 in decimal system is encoded to 1.0049999999999999 in 64-bit binary float; while, 1234567.005 in decimal system is encoded to 1234567.0049999998882413 in 64-bit binary float.

It is worth noting that the maximum binary round-off error is dependent upon (1) the magnitude of the number and (2) the relative machine epsilon (2^-52).

Upvotes: 2

Patrick Berkeley
Patrick Berkeley

Reputation: 2286

Here's a TypeScript implementation of https://stackoverflow.com/a/21323330/916734. It also dries things up with functions, and allows for a optional digit offset.

export function round(rawValue: number | string, precision = 0, fractionDigitOffset = 0): number | string {
  const value = Number(rawValue);
  if (isNaN(value)) return rawValue;

  precision = Number(precision);
  if (precision % 1 !== 0) return NaN;

  let [ stringValue, exponent ] = scientificNotationToParts(value);

  let shiftExponent = exponentForPrecision(exponent, precision, Shift.Right);
  const enlargedValue = toScientificNotation(stringValue, shiftExponent);
  const roundedValue = Math.round(enlargedValue);

  [ stringValue, exponent ] = scientificNotationToParts(roundedValue);
  const precisionWithOffset = precision + fractionDigitOffset;
  shiftExponent = exponentForPrecision(exponent, precisionWithOffset, Shift.Left);

  return toScientificNotation(stringValue, shiftExponent);
}

enum Shift {
  Left = -1,
  Right = 1,
}

function scientificNotationToParts(value: number): Array<string> {
  const [ stringValue, exponent ] = value.toString().split('e');
  return [ stringValue, exponent ];
}

function exponentForPrecision(exponent: string, precision: number, shift: Shift): number {
  precision = shift * precision;
  return exponent ? (Number(exponent) + precision) : precision;
}

function toScientificNotation(value: string, exponent: number): number {
  return Number(`${value}e${exponent}`);
}

Upvotes: 0

Christian C. Salvad&#243;
Christian C. Salvad&#243;

Reputation: 827218

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 round 90% of the time, it will return the rounded value, but for many cases, it doesn't work.

For instance:

2.005.toFixed(2) === "2.00"

UPDATE:

Nowadays, you can use the Intl.NumberFormat constructor. It's part of the ECMAScript Internationalization API Specification (ECMA402). It has pretty good browser support, including even IE11, and it is fully supported in Node.js.

const formatter = new Intl.NumberFormat('en-US', {
   minimumFractionDigits: 2,      
   maximumFractionDigits: 2,
});

console.log(formatter.format(2.005)); // "2.01"
console.log(formatter.format(1.345)); // "1.35"

You can alternatively use the toLocaleString method, which internally will use the Intl API:

const format = (num, decimals) => num.toLocaleString('en-US', {
   minimumFractionDigits: 2,      
   maximumFractionDigits: 2,
});


console.log(format(2.005)); // "2.01"
console.log(format(1.345)); // "1.35"

This API also provides you a wide variety of options to format, like thousand separators, currency symbols, etc.

Upvotes: 1155

user8608712
user8608712

Reputation:

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

Upvotes: -3

remondo
remondo

Reputation: 388

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).

Upvotes: 1

Devner
Devner

Reputation: 7235

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);

Upvotes: 2

David Webster
David Webster

Reputation: 2321

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);
}

Upvotes: 2

MERT DOĞAN
MERT DOĞAN

Reputation: 3106

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.

Upvotes: 4

JONAS MAGALHAES DOS SANTOS
JONAS MAGALHAES DOS SANTOS

Reputation: 11

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>

Upvotes: -5

Vishnu T Asok
Vishnu T Asok

Reputation: 244

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>

Upvotes: 1

ZiTAL
ZiTAL

Reputation: 3581

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/

Upvotes: 1

astorije
astorije

Reputation: 2707

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>

Upvotes: 113

Florian Ignaz E&#223;l
Florian Ignaz E&#223;l

Reputation: 61

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

Upvotes: 5

Miguel Q
Miguel Q

Reputation: 3618

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.

Upvotes: 45

Max G
Max G

Reputation: 66

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

This worked for me: Rounding Decimals in JavaScript

Upvotes: 2

leo_lo
leo_lo

Reputation: 26

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.

Upvotes: 0

Gerard de Visser
Gerard de Visser

Reputation: 8040

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)

Upvotes: 20

Aaron Dake
Aaron Dake

Reputation: 189

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!

Upvotes: 0

Christian L&#230;irbag
Christian L&#230;irbag

Reputation: 338

/*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.
*/

Upvotes: 0

Johnathan Ralls
Johnathan Ralls

Reputation: 141

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

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

Upvotes: 1

Anthony Ruffino
Anthony Ruffino

Reputation: 76

(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.

Upvotes: 0

bamossza
bamossza

Reputation: 3926

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>

Upvotes: 0

HATCHA
HATCHA

Reputation: 600

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

Upvotes: 2

Kamran Ahmed
Kamran Ahmed

Reputation: 12438

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);
}

Upvotes: 1

ow3n
ow3n

Reputation: 6587

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

Upvotes: 5

Imre
Imre

Reputation: 225

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 :)

Upvotes: 3

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