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How to implement Big Int in Javascript?

I am working on open-source project. It doesn’t properly meet its specs due to the representation as JavaScript numbers ie let,const... I want to add support for Int, Long Int, and Big Ints similar to c++.
Can anyone please suggest any resource or approach to achieve this?
Thank you

JavaScript has gained BigInt support as a feature a couple of years ago. By now, most users have browsers new enough to support it: https://caniuse.com/bigint.
If you want to support even older browsers, there are a variety of pure JavaScript implementations with different pros and cons, for example JSBI, MikeMcl's bignumber.js, Peter Olson's BigInteger.js, Yaffle's BigInteger. You can study their sources to learn how they're implemented.
For learning about how native BigInt is implemented, this V8 blog post gives some insight.
Side note: JavaScript is perfectly capable of expressing 32-bit integers à la C++ int/int32_t, no BigInts or libraries are required for that. Bitwise binary operations cause JavaScript numbers to behave like 32-bit integers, so you can write (a + b) | 0 to make the addition behave like a C++ int addition.
If all you need is 64-bit integers, it's not difficult to represent them as pairs of 32-bit numbers. There are also several existing libraries that do that (just use your favorite search engine). If you don't actually need arbitrarily big integers, that may be a nice alternative.

Issue working with numbers in Javascript [duplicate]

This question already has answers here:
Large numbers erroneously rounded in JavaScript
(6 answers)
Closed 5 years ago.
I'm new in developing javascript apps, i have a doubt about a behaviour that i'm going to try to explain.
If i execute:
Number(5555555555555555);
Result: 5555555555555555
But if i execute:
Number(55555555555555555);
Result: 55555555555555550
Anybody can explain to me what is the reason of this? Thanks!!

If you need to work with such big numbers I would suggest you use some of the big integer libraries such as this. The reason this happens as far as I know is the way processors and memory work. It's no related to some "bug" in JS.

Integers (numbers without a period or exponent notation) are accurate up to 15 digits. Javacript simply adds zeros to keep the number accurate in terms of its digit length.
Documentation

converting LARGE string to an integer [duplicate]

How do I parse a 20-digit number using JavaScript and jQuery?

A 20-digit number is generally too big for a JavaScript native numeric type, so you'll need to find a "big number" package to use. Here's one that I've seen mentioned on Stack Overflow and that looks interesting: http://silentmatt.com/biginteger/
That one is just integers. If you need decimal fractions too, you'll have to find something else.
If you just want to check that a 20-digit string looks like a number, and you don't need to know the value, you can do that with a regular expression.

You can't have a 20-digit number in JavaScript - it'll get floated off on you.
You can keep 20 digits (or 200 or 2000) intact as a string, or as an array of digits, but to do any math on it you need a big integer object or library.

Normally you use Number() or parseInt("", [radix]) to parse a string into a real number.
I am guessing you are asking about what happens when the string you parse is above the int - threshold. In this case it greatly depends on what you are trying to accomplish.
There are some libraries that allow working with big numbers such as https://silentmatt.com/biginteger/ - see answer - (did not test it, but it looks OK). Also try searching for BigInt JavaScript or BigMath.
In short: working with VERY large number or exact decimals is a challenge in every programming language and often requires very specific mathematical libraries (which are less convenient and often a lot slower than when you work in "normal" (int/long) areas) - which obviously is not an issue when you REALLY want those big numbers.

Why is this false? Math.ceil(5.0000000000000009) === Math.ceil(5.00000000000000009) // false [duplicate]

This question already has an answer here:
What is the standard solution in JavaScript for handling big numbers (BigNum)?
(1 answer)
Closed 8 years ago.
I'm looking for a Mathematical solution that deals with really (long, big, huge, storms) numbers. I haven't found anything yet, But I don't wanna think that this problem hasn't be solve at this time. I'm looking for an easy Number solution, like Microsoft Excel Precision (30 decimals), or a BigInteger (Java) solution. in Javascript of course.

While looking for an big integer library for an ElGamal crypto implementation I tested several libraries with the following results:
I recommend this one: Tom Wu's jsbn.js (http://www-cs-students.stanford.edu/~tjw/jsbn/)
Comprehensive set of functions and fast
Leemon Baird's big integer library (http://www.leemon.com/crypto/BigInt.js)
Comprehensive set of functions and pretty fast
BUT: Negative number representation is buggy!
bignumber.js (https://github.com/MikeMcl/bignumber.js)
Pretty complete set of functions
BUT: Converting really big numbers from strings into BigNumber objects result in INFINITY
Scheme arithmetic library for JavaScript (https://github.com/jtobey/javascript-bignum)
JS-Implementation of Scheme arithmetic functions
BUT: No function for y= x^e mod n
I haven't tested this by myself: BigNumber (http://jsfromhell.com/classes/bignumber)
Functions for high precision claculations
BUT: It's said to be slow due to internal representation of numbers as strings

There's a BigInteger library for JavaScript available here:
jsbn.js
(Note that I haven't used this myself. Try it and see what you think.)

There is also Silent Matt's library for Big Integers. It does not handle decimals.

JavaScript large number library? [duplicate]

This question already has an answer here:
What is the standard solution in JavaScript for handling big numbers (BigNum)?
(1 answer)
Closed 7 years ago.
Is there a library available in javascript to handle large numbers with accuracy (sort of like what oracle does by storing the number as a string) and allows for operations like add/subtract/multiply/divide/mod/etc ?
Basically I need to add large numbers like 1234567890.1234567890 + 1234567890.987654321 and get a precise result.

As its author, I recommend big.js, 'a small, fast Javascript library for arbitrary-precision arithmetic with decimal numbers'.

There's a few BigInt implementations out there, for example:
JavaScript BigInteger Library
RSA In JavaScript
Layering fixed-point conversion on top of one of them should be pretty easy.
There is also a new decimal type in some implementations, based on a new definition from IEEE 754r — I believe it was part of the (now abandoned) ECMAScript 4 spec, and is carried forward by ECMAScript 3.1/5 and JavaScript 1.9, but I could be wrong on this point.