An arbitrary-precision Decimal type for JavaScript.

WARNING: Version 5 brings significant API changes (see CHANGELOG). Version 4 will continue to be supported.

Features

• Integers and floats
• Simple but full-featured API
• Replicates many of the methods of JavaScript's Number.prototype and Math objects
• Also handles hexadecimal, binary and octal values
• Supports serialization of Decimals to a compact base-88 format for transmission or persistence
• Faster, smaller, and perhaps easier to use than JavaScript versions of Java's BigDecimal
• No dependencies
• Wide platform compatibility: uses JavaScript 1.5 (ECMAScript 3) features only
• Comprehensive documentation and test set

The library is similar to bignumber.js, but here precision is specified in terms of significant digits instead of decimal places, and all calculations are rounded to the precision (similar to Python's decimal module) rather than just those involving division.

This library also adds the trigonometric functions, among others, and supports non-integer powers.

Another major difference is that this library enables multiple Decimal constructors to be created each with their own configuration. This is, however, a significantly larger library than bignumber.js and the even smaller big.js.

Load

The library is the single JavaScript file decimal.js (or minified, decimal.min.js).

It can be loaded using a script tag in an HTML document for the browser

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

or as a Node.js module using require.

var Decimal = require('decimal');

For Node, the library is available from the npm registry

$ npm install decimal.js

To load with AMD loader libraries such as requireJS:

require(['decimal'], function(Decimal) {
    // Use Decimal here in local scope. No global Decimal.
});

Use

In all examples below, var, semicolons and toString calls are not shown. If a commented-out value is in quotes it means toString has been called on the preceding expression.

The library exports a single function object, Decimal, the constructor of Decimal instances.

It accepts a value of type number, string or Decimal.

x = new Decimal(123.4567)
y = new Decimal('123456.7e-3')
z = new Decimal(x)
x.equals(y) && y.equals(z) && x.equals(z)        // true

A value can also be in binary, hexadecimal or octal if the appropriate prefix is included.

x = new Decimal('0xff.f')            // '255.9375'
y = new Decimal('0b10101100')        // '172'
z = x.plus(y)                        // '427.9375'
    
z.toBinary()                         // '0b110101011.1111'
z.toBinary(13)                       // '0b1.101010111111p+8'

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

0.3 - 0.1                     // 0.19999999999999998
x = new Decimal(0.3)
x.minus(0.1)                  // '0.2'
x                             // '0.3'

The methods that return a Decimal can be chained.

x.dividedBy(y).plus(z).times(9).floor()
x.times('1.23456780123456789e+9').plus(9876.5432321).dividedBy('4444562598.111772').ceil()

Many method names have a shorter alias.

x.squareRoot().dividedBy(y).toPower(3).equals(x.sqrt().div(y).pow(3))         // true
x.cmp(y.mod(z).neg()) == 1 && x.comparedTo(y.modulo(z).negated()) == 1        // true

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

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

and many of the methods of JavaScript's Math object are also replicated.

Decimal.sqrt('6.98372465832e+9823')      // '8.3568682281821340204e+4911'
Decimal.pow(2, 0.0979843)                // '1.0702770511687781839'

There are isNaN and isFinite methods, as NaN and Infinity are valid Decimal values,

x = new Decimal(NaN)                                           // 'NaN'
y = new Decimal(Infinity)                                      // 'Infinity'
x.isNaN() && !y.isNaN() && !x.isFinite() && !y.isFinite()      // true

and a toFraction method with an optional maximum denominator argument

z = new Decimal(355)
pi = z.dividedBy(113)        // '3.1415929204'
pi.toFraction()              // [ '7853982301', '2500000000' ]
pi.toFraction(1000)          // [ '355', '113' ]

All calculations are rounded according to the number of significant digits and rounding mode specified by the precision and rounding properties of the Decimal constructor.

As mentioned above, multiple Decimal constructors can be created, each with their own independent configuration which applies to all Decimal numbers created from it.

// Set the precision and rounding of the default Decimal constructor
Decimal.config({ precision: 5, rounding: 4 })

// Create another Decimal constructor, optionally passing in a configuration object
Decimal10 = Decimal.clone({ precision: 10, rounding: 1 })    

x = new Decimal(5)
y = new Decimal10(5)

x.div(3)                           // '1.6667'
y.div(3)                           // '1.666666666'

The value of a Decimal is stored in a floating point format in terms of its digits, exponent and sign.

x = new Decimal(-12345.67);
x.d                            // [ 12345, 6700000 ]    digits (base 10000)
x.e                            // 4                     exponent (base 10)
x.s                            // -1                    sign

For further information see the API reference in the doc directory.

Test

The library can be tested using Node.js or a browser.

The test directory contains the file test.js which runs all the tests when executed by Node, and the file test.html which runs all the tests when opened in a browser.

To run all the tests, from a command-line at the root directory using npm

$ npm test

or at the test directory using Node

$ node test

Each separate test module can also be executed individually, for example, at the test/modules directory

$ node toFraction

Build

For Node, if uglify-js is installed

npm install uglify-js -g

then

npm run build

will create decimal.min.js, and a source map will also be added to the doc directory.

Feedback

M8ch88l@gmail.com

BTC 16MjxmTB5EZxY5Uk9xyhfsu4n9gYxEJYkY

Licence

MIT Expat.

See LICENCE.md