How to prevent rounding of numbers when using toFixed method [duplicate] - javascript

This question already has answers here:
Truncate (not round off) decimal numbers in javascript
(32 answers)
Truncate number to two decimal places without rounding
(43 answers)
Closed 4 months ago.
I am trying to figure out how to prevent rounding of numbers when it comes to decimal precisions. I am currently using the .toFixed(2) method to only display two decimal places after the decimal but it is also rounding this figure. For example, if I had a number 19.528 the method Number(19.528).toFixed(2) will yield 19.53 instead of displaying the value 19.52 . Is there anyway or other method to take care of it so that the number does not round?

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Random Decimals Behind A Number [duplicate]

This question already has answers here:
Is floating point math broken?
(31 answers)
Closed 1 year ago.
Every time I do something like + 1.6 or something that's a decimal, I get a lot of random numbers spammed behind the result. how to avoid?
var test = 1.2345;
console.log(test.toFixed(2))
// It will trim the result to the specified decimal places.
// |----> output will be 1.23 in thid case... It will keep upto 2 decimal places

Javascript "toLocaleString()" function chnages decimals to zero when number is very large [duplicate]

This question already has answers here:
Node.js Maximum Safe Floating-point Number
(4 answers)
What is JavaScript's highest integer value that a number can go to without losing precision?
(21 answers)
Is floating point math broken?
(31 answers)
Closed 2 years ago.
I am developing a react app and i need to format some numbers using toLocaleString function and i realize that the decimal part of the number changes to zero when the number is very
(10000.25).toLocaleString('en',{maximumFractionDigits: 2, minimumFractionDigits: 2});
//Output: 10,000.25
(10000000000000000000.25).toLocaleString('en',{maximumFractionDigits: 2, minimumFractionDigits: 2});
//Output: 10,000,000,000,000,000,000.00
why is this so? is it a bug or am I missing something?
Javascript compiler cannot handle very large numbers. Use Number.MAX_SAFE_INTEGER to check the last number it can handle. Try to consider using string type from the beginning if these numbers are not calculated (Maybe if you get it from an API kind of), or try using BigInt type.
For floating point, the maximum number it can handle to a precision of 1 decimal digit is 562949953421311 and it differs for other digits. This has been referred here. Try using the BigNumber class in your case.

javascript integer bug (number gets reduced by 1) [duplicate]

This question already has answers here:
javascript large integer round because precision? (why?)
(2 answers)
What is JavaScript's highest integer value that a number can go to without losing precision?
(21 answers)
Closed 7 years ago.
number 10205558742352809 gets reduced to 10205558742352808.
What?
TL;DR: Floating-point numbers can be screwy.
Long Answer
Javascript uses 64-bit floating point numbers (IEEE-754). The binary that makes up a floating point number is composed of 3 parts: sign bit (1 bit), exponent field (11 bits), and the significand field (52 bits). There are plenty of sources online that go into further detail about how this works.
If we convert 10205558742352809 to it's binary format then interpret that as hexadecimal for readability we get:
434220F367C941D4
Which is the same thing you'd get for 102...09. Compare that with 102...10:
434220F367C941D5
So 102...09 is not directly representable in IEEE-754 and in fact lies on the border between 102...08 and 102...10.

String to number is wrong [duplicate]

This question already has answers here:
Large numbers erroneously rounded in JavaScript
(6 answers)
Javascript parseInt() with leading zeros
(7 answers)
Closed 7 years ago.
I'm trying to convert a string to number in Javascript, but here is my problem :
var string = "068999999501111443";
parseInt(string); // 68999999501111440
Number(string); // 68999999501111440
Why does this happen and how to fix it ?
Thanks
This is because the number is too large to be stored accurately. It is being stored as a floating point number, which can only store a certain amount of precision. Beyond it's maximum precision, you'll get what look like weird rounding errors.
You'll get similar effects for decimals with a large number of decimal places. This is more well known, as it tends to occur more often, but it's exactly the same effect that is happening here.

Problems with parseInt method [duplicate]

This question already has answers here:
parseInt rounds incorrectly
(2 answers)
Closed 7 years ago.
The parseInt function made my number loose precision: the last two digits changed from 18 to 20:
console.log(parseInt('76561198236425518', 10));
76561198236425520
Why did that happen and how to fix it?
Numbers are stored as floating point with a 53-bit manttissa. This limits the precision you can have to less than what you have in that number of yours, hence it has to round to the nearest floating point number it can represent.
The actual number of bits needed to represent a number N can be calculated as about log2N or, if you're working on a calculator that can't calculate logarithms to base two, logxN/logx2.
The value of log276561198236425518, roughly 56.1, shows that it requires about 56 bits, which is why it's not exact near the end.

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