decimal.js - an arbitrary-precision Decimal type

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decimal.js is an arbitrary-precision Decimal type for JavaScript.
Features

• Faster, smaller, and perhaps easier to use than JavaScript versions of Java’s BigDecimal
• Simple API but full-featured
• Replicates the toExponential, toFixed, toPrecision and toString methods of JavaScript’s Number type
• Includes a toFraction and correctly-rounded exp, ln, log and sqrt functions
• Supports non-integer powers
• Works with numbers with or without fraction digits in bases from 2 to 64 inclusive
• No dependencies
• Wide platform compatibility: uses JavaScript 1.5 (ECMAScript 3) features only
• Comprehensive documentation and test set
• 8 KB minified and gzipped

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 exp, ln and log 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.
1. INCLUDE JS FILE

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

2. 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 numbers.
It accepts a value of type number (up to 15 significant digits only), 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 base from 2 to 36 inclusive can also be specified.

x = new Decimal(1011, 2)             // '11'
y = new Decimal('zz.9', 36)          // '1295.25'
z = x.plus(y)                        // '1306.25'

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 a base can be specified for toString.

x.toString(16)                  // 'ff.8'

There is a toFormat method,

y = new Decimal(1e6)
y.toFormat(2)                // '1,000,000.00'

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' ]

and 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

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.constructor({ precision: 10, rounding: 1 })    

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

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

Decimal.precision                  // 5
Decimal10.precision                // 10

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'

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

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

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