How to round float numbers in javascript?
JavascriptRoundingJavascript Problem Overview
I need to round for example 6.688689 to 6.7, but it always shows me 7.
My method:
Math.round(6.688689);
//or
Math.round(6.688689, 1);
//or
Math.round(6.688689, 2);
But result always is the same 7... What am I doing wrong?
Javascript Solutions
Solution 1 - Javascript
Number((6.688689).toFixed(1)); // 6.7
Solution 2 - Javascript
var number = 6.688689;
var roundedNumber = Math.round(number * 10) / 10;
Solution 3 - Javascript
Use toFixed() function.
(6.688689).toFixed(); // equal to "7"
(6.688689).toFixed(1); // equal to "6.7"
(6.688689).toFixed(2); // equal to "6.69"
Solution 4 - Javascript
Upd (2019-10). Thanks to Reece Daniels code below now available as a set of functions packed in npm-package expected-round (take a look).
You can use helper function from MDN example. Than you'll have more flexibility:
Math.round10(5.25, 0); // 5
Math.round10(5.25, -1); // 5.3
Math.round10(5.25, -2); // 5.25
Math.round10(5, 0); // 5
Math.round10(5, -1); // 5
Math.round10(5, -2); // 5
Upd (2019-01-15). Seems like MDN docs no longer have this helper funcs. Here's a backup with examples:
// Closure
(function() {
/**
* Decimal adjustment of a number.
*
* @param {String} type The type of adjustment.
* @param {Number} value The number.
* @param {Integer} exp The exponent (the 10 logarithm of the adjustment base).
* @returns {Number} The adjusted value.
*/
function decimalAdjust(type, value, exp) {
// If the exp is undefined or zero...
if (typeof exp === 'undefined' || +exp === 0) {
return Math[type](value);
}
value = +value;
exp = +exp;
// If the value is not a number or the exp is not an integer...
if (isNaN(value) || !(typeof exp === 'number' && exp % 1 === 0)) {
return NaN;
}
// If the value is negative...
if (value < 0) {
return -decimalAdjust(type, -value, exp);
}
// Shift
value = value.toString().split('e');
value = Math[type](+(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));
}
// Decimal round
if (!Math.round10) {
Math.round10 = function(value, exp) {
return decimalAdjust('round', value, exp);
};
}
// Decimal floor
if (!Math.floor10) {
Math.floor10 = function(value, exp) {
return decimalAdjust('floor', value, exp);
};
}
// Decimal ceil
if (!Math.ceil10) {
Math.ceil10 = function(value, exp) {
return decimalAdjust('ceil', value, exp);
};
}
})();
Usage examples:
// Round
Math.round10(55.55, -1); // 55.6
Math.round10(55.549, -1); // 55.5
Math.round10(55, 1); // 60
Math.round10(54.9, 1); // 50
Math.round10(-55.55, -1); // -55.5
Math.round10(-55.551, -1); // -55.6
Math.round10(-55, 1); // -50
Math.round10(-55.1, 1); // -60
Math.round10(1.005, -2); // 1.01 -- compare this with Math.round(1.005*100)/100 above
Math.round10(-1.005, -2); // -1.01
// Floor
Math.floor10(55.59, -1); // 55.5
Math.floor10(59, 1); // 50
Math.floor10(-55.51, -1); // -55.6
Math.floor10(-51, 1); // -60
// Ceil
Math.ceil10(55.51, -1); // 55.6
Math.ceil10(51, 1); // 60
Math.ceil10(-55.59, -1); // -55.5
Math.ceil10(-59, 1); // -50
Solution 5 - Javascript
> +(6.688687).toPrecision(2)
6.7
A Number object in JavaScript has a method that does exactly what you need. That method is Number.toPrecision([precision]).
Just like with .toFixed(1) it converts the result into a string, and it needs to be converted back into a number. Done using the + prefix here.
simple benchmark on my laptop:
number = 25.645234 typeof number
50000000 x number.toFixed(1) = 25.6 typeof string / 17527ms
50000000 x +(number.toFixed(1)) = 25.6 typeof number / 23764ms
50000000 x number.toPrecision(3) = 25.6 typeof string / 10100ms
50000000 x +(number.toPrecision(3)) = 25.6 typeof number / 18492ms
50000000 x Math.round(number*10)/10 = 25.6 typeof number / 58ms
string = 25.645234 typeof string
50000000 x Math.round(string*10)/10 = 25.6 typeof number / 7109ms
Solution 6 - Javascript
If you not only want to use toFixed() but also ceil() and floor() on a float then you can use the following function:
function roundUsing(func, number, prec) {
var tempnumber = number * Math.pow(10, prec);
tempnumber = func(tempnumber);
return tempnumber / Math.pow(10, prec);
}
Produces:
> roundUsing(Math.floor, 0.99999999, 3)
0.999
> roundUsing(Math.ceil, 0.1111111, 3)
0.112
UPD:
The other possible way is this:
Number.prototype.roundUsing = function(func, prec){
var temp = this * Math.pow(10, prec)
temp = func(temp);
return temp / Math.pow(10, prec)
}
Produces:
> 6.688689.roundUsing(Math.ceil, 1)
6.7
> 6.688689.roundUsing(Math.round, 1)
6.7
> 6.688689.roundUsing(Math.floor, 1)
6.6
Solution 7 - Javascript
My extended round function:
function round(value, precision) {
if (Number.isInteger(precision)) {
var shift = Math.pow(10, precision);
// Limited preventing decimal issue
return (Math.round( value * shift + 0.00000000000001 ) / shift);
} else {
return Math.round(value);
}
}
Example Output:
round(123.688689) // 123
round(123.688689, 0) // 123
round(123.688689, 1) // 123.7
round(123.688689, 2) // 123.69
round(123.688689, -2) // 100
round(1.015, 2) // 1.02
Solution 8 - Javascript
There is the alternative .toLocaleString() to format numbers, with a lot of options regarding locales, grouping, currency formatting, notations. Some examples:
Round to 1 decimal, return a float:
const n = +6.688689.toLocaleString('fullwide', {maximumFractionDigits:1})
console.log(
n, typeof n
)
Round to 2 decimals, format as currency with specified symbol, use comma grouping for thousands:
console.log(
68766.688689.toLocaleString('fullwide', {maximumFractionDigits:2, style:'currency', currency:'USD', useGrouping:true})
)
Format as locale currency:
console.log(
68766.688689.toLocaleString('fr-FR', {maximumFractionDigits:2, style:'currency', currency:'EUR'})
)
Round to minimum 3 decimal, force zeroes to display:
console.log(
6.000000.toLocaleString('fullwide', {minimumFractionDigits:3})
)
Percent style for ratios. Input * 100 with % sign
console.log(
6.688689.toLocaleString('fullwide', {maximumFractionDigits:2, style:'percent'})
)
Solution 9 - Javascript
See below
var original = 28.59;
var result=Math.round(original*10)/10 will return you returns 28.6
Hope this is what you want..
Solution 10 - Javascript
I have very good solution with if toFixed() is not working.
function roundOff(value, decimals) {
return Number(Math.round(value+'e'+decimals)+'e-'+decimals);
}
Example
roundOff(10.456,2) //output 10.46
Solution 11 - Javascript
float(value,ndec);
function float(num,x){
this.num=num;
this.x=x;
var p=Math.pow(10,this.x);
return (Math.round((this.num).toFixed(this.x)*p))/p;
}
Solution 12 - Javascript
I think this function can help.
function round(value, ndec){
var n = 10;
for(var i = 1; i < ndec; i++){
n *=10;
}
if(!ndec || ndec <= 0)
return Math.round(value);
else
return Math.round(value * n) / n;
}
round(2.245, 2) //2.25
round(2.245, 0) //2
Solution 13 - Javascript
if you're under node.js context, you can try mathjs
const math = require('mathjs')
math.round(3.1415926, 2)
// result: 3.14
Solution 14 - Javascript
+((6.688689 * (1 + Number.EPSILON)).toFixed(1)); // 6.7
+((456.1235 * (1 + Number.EPSILON)).toFixed(3)); // 456.124
Solution 15 - Javascript
Math.round((6.688689 + Number.EPSILON) * 10) / 10
Solution stolen from https://stackoverflow.com/a/11832950/2443681
This should work with nearly any float value. It doesn't force decimal count though. It's not clear whether this was a requirement. Should be faster than using toFixed(), which has other issues as well based on the comments to other answers.
A nice utility function to round in needed decimal precision:
const roundToPrecision = (value, decimals) => {
const pow = Math.pow(10, decimals);
return Math.round((value + Number.EPSILON) * pow) / pow;
};
Solution 16 - Javascript
I think below function can help
function roundOff(value,round) {
return (parseInt(value * (10 ** (round + 1))) - parseInt(value * (10 ** round)) * 10) > 4 ? (((parseFloat(parseInt((value + parseFloat(1 / (10 ** round))) * (10 ** round))))) / (10 ** round)) : (parseFloat(parseInt(value * (10 ** round))) / ( 10 ** round));
}
usage : roundOff(600.23458,2); will return 600.23
Solution 17 - Javascript
Minor tweak to this answer:
function roundToStep(value, stepParam) {
var step = stepParam || 1.0;
var inv = 1.0 / step;
return Math.round(value * inv) / inv;
}
roundToStep(2.55, 0.1) = 2.6
roundToStep(2.55, 0.01) = 2.55
roundToStep(2, 0.01) = 2
Solution 18 - Javascript
If you're using Browserify today, you're going to have to try: roundTo a very useful NPM lib