Parse Float has a rounding limit? How can I fix this? - javascript

I set up a system that parses a compact data string into JSON. I'm using a 19 digit number to store ids. Unfortunately any number greater than 17 digits, parseFloat() rounds the last few digits.
This breaks the whole data string. Can I fix this?
For example 8246295522085275215 gets turned into 8246295522085276000. Why is this?
http://jsfiddle.net/RobertWHurst/mhZ7Q/

JavaScript has only one numeric type, which is an IEEE 754 double precision floating-point. That means, you have a maximum of 52 bits of precision, which is a bit more than 15 decimal places.
If you need more precision than that, you have to use a bignum library or work with strings.

Numbers in JavaScript lose precision if they are higher than a certain value.
According to http://www.hunlock.com/blogs/The_Complete_Javascript_Number_Reference, integers are only reliable up to 15 digits (9 * 10^15 to be exact).

Try one of these
1. Use a string
2. Split your number in two and save the smaller parts to an array
3. Bignum library
4. Use a smaller number if you can

Related

Js how to increase a big number [duplicate]

This question already has answers here:
What is JavaScript's highest integer value that a number can go to without losing precision?
(21 answers)
Closed 4 months ago.
How to increase this number(you can try it on the browser console):
36893488147419103000 + 1
The result of this is:
36893488147419103000
The number stays the same no changes to it why is that? and how can I increase it by 1?
For big integers you should use the BigInt (Big Integer) type.
Note 1: you almost always cannot mix BigInt numbers with Numbers (eg for math operations) without first performing an explicit conversion.
Note 2: JSON does not currently natively support BigInt values. As a workaround you can use strings (eg. '1n' for the values and then use a reviver function when calling JSON.parse.
JavaScript currently only has two numeric types: double-precision IEEE 754 floating point Numbers, and Big Integers which can be used to represent arbitrarily large integers. You can declare a BigInt number literal using the suffix n, eg. 1n.
IEEE 754 Numbers can "only" accurately represent integers up to and including Number.MAX_SAFE_INTEGER, which has a value of 2^53 - 1 or 9,007,199,254,740,991 or ~9 quadrillion.
From MDN:
Double precision floating point format only has 52 bits to represent the mantissa, so it can only safely represent integers between -(253 – 1) and 253 – 1. "Safe" in this context refers to the ability to represent integers exactly and to compare them correctly. For example, Number.MAX_SAFE_INTEGER + 1 === Number.MAX_SAFE_INTEGER + 2 will evaluate to true, which is mathematically incorrect. See Number.isSafeInteger() for more information.
A "Decimal" number type, that will be able to represent arbitrarily precise decimal numbers, is under development.
Obviously the number is internally represented as a floating point number.When the value you want do add to this number is less then the value of the least significant bit, it will not change the the value.
The only way would be to use floating point numbers with a higher resolution i.e. with a higher number of significant bits.
Double precision floating point format only has 52 bits to represent the mantissa, so it can only safely represent integers between -(253 – 1) and 253 – 1. See Number.MAX_SAFE_INTEGER. Larger numbers may not be able to be represented exactly.

Postgres and Javascript require to support more than 15 digits including decimal

I need to store values in PostgreSQL database where 12 numbers and 6 decimal. According to PostgreSQL it provides numeric datatype. I created a field with numeric(18,6), but when I am entering value, it is just accepting 15 digits values total.
For e.g.
If i try to store number 123456789123.123456, it truncates number and stores only 123456789123.123.
In JavaScript, when I am trying to parse a string of 18 digits including 6 decimals it returns only 17 digits, 12 numbers and 5 decimals.
For e.g.
var number = "123456789123.123456"
console.log(parseFloat(number));
it prints only 123456789123.12346
Is there any solution about this?
This is a limitation of the double-precision floating point data type and is not unique to JavaScript or Postgres. Postgres can use the same double-precision floating point type, or, as you have done, support an arbitrary precision number which is stored in a different format.
JavaScript only has one numeric data type: double-precision floating point.
Wikipedia - IEEE 754 Floating Point Standard
Keep in mind that this is a precision limitation, not "17 digits". You can successfully store 0.0000000000000003939393928293 or 8949493210129000000000000000000000000000.
If you need to work with numbers of greater precision, you can use a library like bignumber.js. You lose the ability to use the simple operators, so num3 = num1 + num2 becomes num3 = num1.plus(num2), but it should do what you need.
bignumber.js

Converting big number string to number

What way i can convert string with 16 digits and 2 fraction value to number ?
Currently when I try to convert Number('1234567890123456.12') will became to 1234567890123456. fraction values will be gone.
I just want to confirm without using any third party lib can i convert this string to number ?
Unfortunately not. Javascript represents it's numbers using double precision floating point numbers. At 16 digits, it will only be able to store the integer component and not the part after the decimal point. You will need a bignum library to use this value.
EDIT: for reference the biggest integer you can use in JavaScript is 9,007,199,254,740,991
EDIT2: Thanks to Jeremy you can use a library like bignumberJS.
Your number has too many algorisms, I've created an example that simulates in the first position of the array the maximum length possible in javascript.
var nums = [
"12345678910111.12",
"1.5323",
"-42.7789"
];
nums.forEach(function(n) {
console.log(parseFloat(n).toFixed(2));
});
https://jsfiddle.net/7zzz1qzt/
I have faced issue to convert 18 digit string number to number. It is convert all digit to 0 after 16 digit. I have apply below code. it is working fine for me.
[{"id":${id},"name":"${name}"}]

Why is JavaScript's number *display* for large numbers inaccurate?

So in JavaScript, 111111111111111111111 == 111111111111111110000. Just type any long number – at least about 17 digits – to see it in action ;-)
That is because JavaScript uses double-precision floating-point numbers, and certain very long numeric literals can not be expressed accurately. Instead, those numbers get rounded to the nearest representable number possible. See e.g. What is JavaScript's highest integer value that a Number can go to without losing precision?
However, doing the math according to IEEE-754, I found out that every number inside [111111111111111106560, 111111111111111122944] will be replaced by 111111111111111114752 internally. But instead of showing this ...4752 number, it gets displayed as 111111111111111110000. So JavaScript is showing those trailing zeros which obfuscates the real behavior. This is especially annoying because even numbers like 263, which are accurately representable, get "rounded" as described.
So my question is: Why does JavaScript behave like this when displaying the number?
JavaScript integers can only be +/- 253, which is:
9007199254740992
One of your numbers is
111111111111111106560
which is considerably outside of the range of numbers that can accurately represented as an integer.
This follows the IEEE 754:
Sign bit: 1 bit
Exponent width: 11 bits
Significand precision: 53 bits (52 explicitly stored)
EDIT
The Display of numbers is sometimes rounded by the JavaScript engine, yes. However, that can be over-ridden using the toFixed method. (Warning, toFixed is known to be broken under some versions of IE).
In your console, type:
111111111111111122944..toFixed(0)
"111111111111111114752"

parseFloat of string longer than 16 characters

Does parseFloat of a string have a limit to how many characters the string can be? I don't see anything about a limit here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseFloat
But running the following in console seems to show results I wasn't expecting.
parseFloat('1111111111111111'); // 16 characters long
// result 1111111111111111
parseFloat('11111111111111111'); // 17 characters long
// result 11111111111111112
Can anyone break this down for me?
In Javascript, floating point numbers are stored as double precision values. These have about 16 significant digits, which means that a 17-digit number won't necessarily be stored exactly.
You can supply numbers of any length to parseFloat(), but it won't be possible to store anything larger than 1.79769×10308, which is the largest possible value that can be stored in a double precision variable.
I'd recommend reading this if you have time: What Every Computer Scientist Should Know About Floating-Point Arithmetic

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