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How does JavaScript engine compute arithmetic expression? [duplicate]

This question already has answers here:
Why does changing the sum order returns a different result?
(7 answers)
In which order should floats be added to get the most precise result?
(11 answers)
How to deal with floating point number precision in JavaScript?
(47 answers)
Closed 5 months ago.
Quick summary - I was running a piece of code(in React application) where I am summing up decimal values entered by a user. One of the conditions to move to next page is if the sum equals 100
Problem - In one case, the sum of all values (a+b+c+d+e+f) is being computed to 99.99999999999997 even though the summation(over a calculator) is 100. But when I change the summation order to a+d+e+f+b+c, the sum is correctly computed to 100.
Please find below code samples -
Wrong summation -
const result = [15+10.4+1.9+1.9+4.9+2.8+6.8+2+4.9+2.8+2.5+2.8+4.8+6.5+15+15].reduce((sum, val) => {return sum+val}, 0)
console.log(result) //99.99999999999997
Correct summation -
const result = [15+10.4+4.9+2.8+6.8+2+4.9+2.8+2.5+2.8+4.8+6.5+15+15+1.9+1.9].reduce((sum, val) => {return sum+val}, 0)
console.log(result) //100
Questions -
How does JavaScript engine compute?
How to compute to 100 always (without using ceil, floor or round methods because Math.round(99.6) is also equal to 100.

Getting long decimals from arithmetic operator [duplicate]

This question already has answers here:
Is floating point math broken?
(31 answers)
Precise Financial Calculation in JavaScript. What Are the Gotchas?
(8 answers)
Closed 5 years ago.
I have a piece of code that is pulling data from a SharePoint list from I'm using SPServices and this code then pulls from the Spent column and adds up all the numbers and then puts it in an array however I'm getting some weird results.
none of the numbers it pulls through have more than 2 decimal places(it's a finance column) however I'm getting totals like 57062.229999999996 and 151704.58000000002
I've tried using .toFixed(2) on to mynumber and parseFloat(SpentFix)
and then converting back to a number and I get the same results.
Also the reason why I have a .substring(7) is because the spend column is a computed field so when pulling data float,# is a the start of each entry for some reason
if anyone can help that would be great.
var SpentFix = $(this).attr("ows_Spent").substring(7);
if (SpentFix != undefined) {
var mynumber = parseFloat(SpentFix)
SLarray[counter][1] += mynumber;
}

Extra numbers being added when decrementing value from number with JavaScript [duplicate]

This question already has answers here:
How to deal with floating point number precision in JavaScript?
(47 answers)
Closed 5 years ago.
I'm trying to decrement "0.01" from a number, it works fine the first time, but when I try to decrement one more time it adds some extra numbers.
Here is my JavaScript code:
function decrement() {
var credits_sidebar = $('#credits_sidebar').html();
var credits_update = credits_sidebar - 0.01;
$("#credits_sidebar").fadeOut('');
$("#credits_sidebar").html(credits_update);
$("#credits_sidebar").fadeIn('');
}
If you click once on the decrement button it works, but if you click another time, the number will be "95.97999999999999" it should be 95.98 instead.
Here's an example JsFiddle:
https://jsfiddle.net/rozvnay1/

var credits_update = (credits_sidebar - 0.01).toFixed(2)
JSFiddle demo: https://jsfiddle.net/8eakhn4L/1/

This is a problem with floating point value representation.
You should consider using
Math.round((credits_sidebar - 0.01)* 100)) / 100

This behavior is normal and expected because of the way floating point math is done in JavaScript.
However what you simply can do is multiply your number by a factor of 100 to make it a whole number that needs to be decremented then you can do the decrement and divide the result by 100 to get the correct decimal answer.

You need to update this for working of code:
var credits_update = (credits_sidebar - 0.01).toFixed(2);

Adding decimal to a number multiplies it by ten in Javascript

I'm having a problem with adding numbers in javascript. I have a variable that keeps track of full number (currentfloatx) and a variable that keeps track of the floored version of that number (newintx). I'm trying to add .25 to currentfloatx, but for some reason its multiplying the number by 10. Does anyone know why it's doing this? Is there something about how javascript is handling these number that I'm missing? Thanks.
//currentfloatx is currently set to 6
alert(currentfloatx + .25); //returns 60.25
alert(currentfloatx); //returns 6
newintx = Math.floor(currentfloatx + .25);
alert(newintx); //returns 60.25

The only way I can think of that would make this happen is if currfloatx holds a string (eg., "6"). This would make currfloatx + .25 be the equivalent of "6" + "0.25", or "60.25".

Division inaccurate in Javascript? [duplicate]

This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Elegant workaround for JavaScript floating point number problem
If I perform the following operation in Javascript:
0.06120*400
The result is 24.48.
However, if I do this:
24.48/400
The result is:
0.061200000000000004
JSFiddle: http://jsfiddle.net/zcDH7/
So it appears that Javascript rounds things differently when doing division and multiplication?
Using my calculator, the operation 24.48/400 results in the correct answer of 0.0612.
How should I deal with Javascript's inaccurate division? I can't simply round the number off, because I will be dealing with numbers of varying precision.
Thanks for your advice.

You can get the correct result with simply using:
var a = 24.48/400;
console.log(a.toFixed(6));
And because typeof a.toFixed(6) === 'string' you can:
var a = 24.48/400;
console.log(parseFloat(a.toFixed(6)));
The argument of toFixed is the number of decimals you want.