Number.prototype.toFixed is a function designed to format a number before printing it out. It's from the family of toString, toExponential and toPrecision.
To round a number, you would do this:
someNumber = 42.008;
someNumber = Math.round( someNumber * 1e2 ) / 1e2;
someNumber === 42.01;
// if you need 3 digits, replace 1e2 with 1e3 etc.
// or just copypaste this function to your code:
function toFixedNumber(num, digits, base){
const pow = Math.pow(base ?? 10, digits);
return Math.round(num*pow) / pow;
}
Why isn't this function included in the JavaScript's standard library? Because floating point numbers are hard! Many decimal numbers cannot be directly represented by base-two floats – that's why 0.09 + 0.01 !== 0.1 but 0.09999999999999999. If developers were given a tool which is supposed to round floats to decimal places, they'd (wrongly) assume that it really returns a decimal number, when it in fact returns the closest representable double-precision base-two float.
types - How can I round a number in JavaScript? .toFixed() returns a string? - Stack Overflow
This is why you should not using "toFixed" to rounding a number to the nearest integer.
Javascript toFixed function - Stack Overflow
javascript - Using toFixed(2) and math round to get correct rounding - Stack Overflow
Number.prototype.toFixed is a function designed to format a number before printing it out. It's from the family of toString, toExponential and toPrecision.
To round a number, you would do this:
someNumber = 42.008;
someNumber = Math.round( someNumber * 1e2 ) / 1e2;
someNumber === 42.01;
// if you need 3 digits, replace 1e2 with 1e3 etc.
// or just copypaste this function to your code:
function toFixedNumber(num, digits, base){
const pow = Math.pow(base ?? 10, digits);
return Math.round(num*pow) / pow;
}
Why isn't this function included in the JavaScript's standard library? Because floating point numbers are hard! Many decimal numbers cannot be directly represented by base-two floats – that's why 0.09 + 0.01 !== 0.1 but 0.09999999999999999. If developers were given a tool which is supposed to round floats to decimal places, they'd (wrongly) assume that it really returns a decimal number, when it in fact returns the closest representable double-precision base-two float.
I've solved this problem by changing this:
someNumber = someNumber.toFixed(2)
...to this:
someNumber = +someNumber.toFixed(2);
However this will convert the number to a string and parse it again, which will have a significant impact on performance. If you care about performance or type safety, check the the other answers as well.
console.log(+(123.455).toFixed(2))
--> The output is 123.45 (wrong)
console.log(Math.round(123.455 * 100) / 100)
--> The output is 123.46 (correct)
-----------------------------------------------------------------------------
Some peoples said "toFixed" is rounding down the number. This is not true.
> +(123.45).toFixed(1)
123.5 (rounding up)
> +(123.445).toFixed(2)
123.44 (rounding down)
As there is no difference between integers and floats in JavaScript, here is my quick'n'dirty approach:
theNumber.toFixed(2).replace(".00", "");
Or something generic:
myToFixed = function (n, digits) {
digits = digits || 0;
return n.toFixed(digits).replace(new RegExp("\\.0{" + digits + "}"), "");
}
myToFixed(32.1212, 2) --> "32.12"
myToFixed(32.1212, 0) --> "32"
myToFixed(32, 2) --> "32"
myToFixed(32.1, 2) --> "32.10"
You don't need Math.round():
var toFixed = function(val, n) {
var result = val.toFixed(n);
if (result == val)
return val.toString();
return result;
}
toFixed(3.123, 2) --> "3.12"
toFixed(3, 2) --> "3"
How about this?
function wacky_round(number, places) {
var multiplier = Math.pow(10, places+2); // get two extra digits
var fixed = Math.floor(number*multiplier); // convert to integer
fixed += 44; // round down on anything less than x.xxx56
fixed = Math.floor(fixed/100); // chop off last 2 digits
return fixed/Math.pow(10, places);
}
1.5554 => 1.55
1.5555 => 1.55
1.5556 => 1.56
1.5651 => 1.56
So, that works, but I think you'll find that it's not a generally-accepted way to round. http://en.wikipedia.org/wiki/Rounding#Tie-breaking
And standard function
fixedTo = function (number, n) {
var k = Math.pow(10, n);
return (Math.round(number * k) / k);
}
and then call
fixedTo(1.5555, 2) // 1.56
fixedTo(1.5555, 2) // 1.556
fixedTo(0.615, 2) // 0.62