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bi-fraction provides a fraction number abstraction for working with numbers in Javascript.

One benefit of using BigInt with the Fraction abstraction is that it eliminates the need for rounding for rational numbers. It can perform math operations on fractions without losing any precision. The ensures that all rational math operations are exact, allowing you to maintain the highest level of accuracy.

When doing math operations that produce irrational numbers or converting a Fraction to other representations such as strings or numbers, bi-fraction offers you "arbitrary precision". This means that you have the freedom to specify the desired precision, enabling you to obtain as many precision as needed.

bi-fraction support 9 rounding modes as in bignumber.js and decimal.js. Since rational numbers can be represented precisely with fraction numbers, rational math operations (e.g., add, sub, mul, div) never incur the rounding overhead. Rounding is only necessary when performing operations that produce irrational numbers (e.g., sqrt, sin, cos) or converting fractions to other representations.

The Fraction class ensure reliable and predictable behavior throughout its methods. Lots methods of the Fraction class accept an other: FractionIsh parameter as input. The FractionIsh type is defined as type FractionIsh = Fraction | NumberIsh.

A NumberIsh represents a value that can be converted to a number. It can be either a number, bigint, or string that can be successfully converted using the Number(str) function. However, if Number(str) returns NaN, indicating a failed conversion, the input str is considered an invalid NumberIsh.

In such cases, instead of returning NaN, all methods of the Fraction class will throw an error to indicate that the input is not a valid NumberIsh.

Built on top of BigInt, Fraction follows the same behavior of BigInt. In contrast to plain JavaScript numbers, which return Infinity or -Infinity when divided by zero, BigInt and therefore Fraction throw an error.

bi-fraction API Doc

# install with npm
npm install bi-fraction

# install with yarn
yarn add bi-fraction

# install with pnpm
pnpm add bi-fraction

import { Fraction, RoundingMode } from 'bi-fraction';

0.1 + 0.2 === 0.3; // false
new Fraction(0.1).add(0.2).eq(0.3); // true

1e18 + 1 === 1e18; // true
new Fraction(1e18).add(1).eq(1e18); // false
new Fraction('1e18').add(1).eq('1e18'); // false

// new Fraction(numerator: FractionIsh, denominator?: FractionIsh = 1)
const a = new Fraction('0.1').div('0.3');
q.eq(new Fraction(1, 3)); // true

const bigNumber = new Fraction(
  '10000000000000000000000000000000001.0000000001',
);
const bigInteger = new Fraction(1_000_000_000n);
bigNumber
  .mul(bigInteger)
  .eq(new Fraction(100000000000000000000000000000000010000000001n)); // true

const x = new Fraction(1234.5);
x.toFixed(0); // '1235'
x.toFixed(0, { roundingMode: RoundingMode.ROUND_DOWN }); // '1234'
x.toFixed(3); // '1234.500'
x.toFixed(3, { trailingZero: false }); // '1234.5'

const z = x.mul(x); // 1523990.25

z.toPrecision(4); // '1524000'
z.toPrecision(4, { roundingMode: RoundingMode.ROUND_DOWN }); // '1523000'
z.toPrecision(9); // '1523990.25'
z.toPrecision(10); // '1523990.250'

z.toFormat({  decimalPlaces: 0 }); // '1,523,990';
z.toFormat({ format: { groupSize: 4 } }); // '152,3990'
z.toFormat({ decimalPlaces: 3, { groupSeparator: '_' }}); // '1_523_990.250'
z.toFormat({ decimalPlaces: 3, trailingZero: false, { groupSeparator: '_' }}); // '1_523_990.25'

pnpm test
pnpm coverage