big.js

What is big.js?

The big.js npm package is a library for arbitrary-precision decimal arithmetic. It allows you to perform calculations on numbers with a large number of digits without losing precision, which is a common issue with JavaScript's native Number type.

What are big.js's main functionalities?

Arithmetic Operations

Perform precise addition, subtraction, multiplication, and division operations.

{"addition": "new Big('0.1').plus(new Big('0.2')).toString()", "subtraction": "new Big('0.3').minus(new Big('0.1')).toString()", "multiplication": "new Big('0.2').times(new Big('0.3')).toString()", "division": "new Big('0.3').div(new Big('0.2')).toString()"}

Comparison Operations

Compare two Big numbers to determine equality, or whether one is greater than or less than the other.

{"equals": "new Big('1.0').eq(new Big('1.00'))", "greaterThan": "new Big('2').gt(new Big('1.9999'))", "lessThan": "new Big('0.1').lt(new Big('0.2'))"}

Rounding

Round Big numbers to a specified number of decimal places, or convert a Big number to a fixed-point notation string.

{"round": "new Big('0.12345').round(2).toString()", "toFixed": "new Big('0.12345').toFixed(2)"}

Configuration

Configure the number of decimal places for rounding and the rounding mode (e.g., round half up, round down, etc.).

{"setDP": "Big.DP = 10", "setRM": "Big.RM = 1"}

Other packages similar to big.js

bignumber.js

bignumber.js is another arbitrary-precision decimal and non-decimal arithmetic library with similar functionality to big.js. It provides more features, such as support for non-decimal bases, but it might be slower for some operations due to its broader scope.

decimal.js

decimal.js is a library for arbitrary-precision arithmetic that is similar to big.js but with additional features like trigonometric and logarithmic functions, which big.js does not have. It also allows for immutable Decimal instances.

fraction.js

fraction.js is focused on rational numbers (fractions) and provides arithmetic operations for them. It is different from big.js, which deals with decimal numbers, but it can be used for high-precision calculations where representing numbers as fractions is more appropriate.

README

big.js

A small, fast JavaScript library for arbitrary-precision decimal arithmetic.

Features

• Simple API
• Faster, smaller and easier-to-use than JavaScript versions of Java's BigDecimal
• Only 6 KB minified
• Replicates the toExponential, toFixed and toPrecision methods of JavaScript Numbers
• Stores values in an accessible decimal floating point format
• Comprehensive documentation and test set
• No dependencies
• Uses ECMAScript 3 only, so works in all browsers

The little sister to bignumber.js and decimal.js. See here for some notes on the difference between them.

Install

The library is the single JavaScript file big.js or the ES module big.mjs.

Browsers

Add Big to global scope:

<script src='path/to/big.js'></script>

ES module:

<script type='module'>
import Big from './path/to/big.mjs';

Get a minified version from a CDN:

<script src='https://cdn.jsdelivr.net/npm/big.js@6.2.2/big.min.js'></script>

Node.js

$ npm install big.js

CommonJS:

const Big = require('big.js');

ES module:

import Big from 'big.js';

Deno

import Big from 'https://raw.githubusercontent.com/mikemcl/big.js/v6.2.2/big.mjs';
import Big from 'https://unpkg.com/big.js@6.2.2/big.mjs';

Use

In the code examples below, semicolons and toString calls are not shown.

The library exports a single constructor function, Big.

A Big number is created from a primitive number, string, or other Big number.

x = new Big(123.4567)
y = Big('123456.7e-3')                 // 'new' is optional
z = new Big(x)
x.eq(y) && x.eq(z) && y.eq(z)          // true

In Big strict mode, creating a Big number from a primitive number is disallowed.

Big.strict = true
x = new Big(1)                         // TypeError: [big.js] Invalid number
y = new Big('1.0000000000000001')
y.toNumber()                           // Error: [big.js] Imprecise conversion

A Big number is immutable in the sense that it is not changed by its methods.

0.3 - 0.1                              // 0.19999999999999998
x = new Big(0.3)
x.minus(0.1)                           // "0.2"
x                                      // "0.3"

The methods that return a Big number can be chained.

x.div(y).plus(z).times(9).minus('1.234567801234567e+8').plus(976.54321).div('2598.11772')
x.sqrt().div(y).pow(3).gt(y.mod(z))    // true

Like JavaScript's Number type, there are toExponential, toFixed and toPrecision methods.

x = new Big(255.5)
x.toExponential(5)                     // "2.55500e+2"
x.toFixed(5)                           // "255.50000"
x.toPrecision(5)                       // "255.50"

The arithmetic methods always return the exact result except div, sqrt and pow (with negative exponent), as these methods involve division.

The maximum number of decimal places and the rounding mode used to round the results of these methods is determined by the value of the DP and RM properties of the Big number constructor.

Big.DP = 10
Big.RM = Big.roundHalfUp

x = new Big(2);
y = new Big(3);
z = x.div(y)                           // "0.6666666667"
z.sqrt()                               // "0.8164965809"
z.pow(-3)                              // "3.3749999995"
z.times(z)                             // "0.44444444448888888889"
z.times(z).round(10)                   // "0.4444444445"

The value of a Big number is stored in a decimal floating point format in terms of a coefficient, exponent and sign.

x = new Big(-123.456);
x.c                                    // [1,2,3,4,5,6]    coefficient (i.e. significand)
x.e                                    // 2                exponent
x.s                                    // -1               sign

For advanced usage, multiple Big number constructors can be created, each with an independent configuration.

For further information see the API reference documentation.

Minify

To minify using, for example, npm and terser

$ npm install -g terser

$ terser big.js -c -m -o big.min.js

Test

The test directory contains the test scripts for each Big number method.

The tests can be run with Node.js or a browser.

Run all the tests:

$ npm test

Test a single method:

$ node test/toFixed

For the browser, see runner.html and test.html in the test/browser directory.

big-vs-number.html is a old application that enables some of the methods of big.js to be compared with those of JavaScript's Number type.

TypeScript

The DefinitelyTyped project has a Typescript type definitions file for big.js.

$ npm install --save-dev @types/big.js

Any questions about the TypeScript type definitions file should be addressed to the DefinitelyTyped project.

Licence

MIT

Contributors

Financial supporters

Thank you to all who have supported this project via Open Collective, particularly Coinbase.

Changelog

6.2.2

• 10/09/24
• #212 Bugfix: sqrt error when Big.strict is true.