Decimal.js

❌ Deprecation Notice ❌

This package is deprecated. Please refer to the the Decimal.js package available at Decimal.js Documentation for updated features and support.

Simple decimal arithmetic for the browser and node.js!

Why?

Why don't my numbers, like 0.1 + 0.2 add up to a nice round 0.3,
and instead I get a weird result like 0.30000000000000004?

Because internally, computers use a format (binary floating-point)
that cannot accurately represent a number like 0.1, 0.2 or 0.3 at all.

Source : http://floating-point-gui.de/

I wrote this because I needed to do simple computation in the browser and I couldn't find a lightweight library to do it.

How to use?

In the browser

<script src="lib/decimal.js"></script>

In Node.js / Deno

npm install decimal

then in your program

let Decimal = require('decimal');

Examples

Addition

// Regular JavaScript
>>> 0.1 + 0.2
0.30000000000000004

// Using Decimal.js
>>> Decimal('0.1').add('0.2').toString()
'0.3'

// Static method
>>> Decimal.add('0.1', '0.2').toString()
'0.3'

Subtraction

// Regular JavaScript
>>> 0.3 - 0.1
0.19999999999999998

// Using Decimal.js
>>> Decimal('0.3').sub('0.1').toString()
'0.2'

// Static method
>>> Decimal.sub('0.3', '0.1').toString()
'0.2'

Multiplication

// Regular JavaScript
>>> 4.01 * 2.01
8.060099999999998

// Using Decimal.js
>>> Decimal('4.01').mul('2.01').toString()
'8.0601'

// Static method
>>> Decimal.mul('4.01', '2.01').toString()
'8.0601'

Division

// Regular JavaScript
>>> 1.21 / 0.1
12.100000000000001

// Using Decimal.js
>>> Decimal('1.21').div('0.1').toString()
'12.1'

// Static method
>>> Decimal.div('1.21', '0.1').toString()
'12.1'

// Division by zero
>>> Decimal('1.21').div('0').toString()
node:internal/modules/run_main:122
    triggerUncaughtException(...)
    ^
[DivisionByZeroError: Division by zero]

Can I help?

Of course you can, I suck at math, and this implementation is very naive. If you are a math Guru and you see something wrong or a way to simplify things you can send in a pull request.

Methods

Decimal(n)

Create a new Decimal from n. n can be a string, integer, or another Decimal.

Basic Operations

.toString()

Returns the Decimal instance as a string.

>>> Decimal('123.456').toString()
'123.456'

.toNumber()

Turn a Decimal into a Number.

>>> Decimal('123.456').toNumber()
123.456

.add(n)

Return a new Decimal containing the instance value plus n.

>>> Decimal('0.1').add('0.2').toString()
'0.3'

.sub(n)

Return a new Decimal containing the instance value minus n.

>>> Decimal('0.3').sub('0.1').toString()
'0.2'

.mul(n)

Return a new Decimal containing the instance value multiplied by n.

>>> Decimal('4.01').mul('2.01').toString()
'8.0601'

.div(n)

Return a new Decimal containing the instance value integrally divided by n.

>>> Decimal('1.21').div('0.1').toString()
'12.1'

Numeric Operations

.abs()

Returns a new Decimal containing the absolute value.

>>> Decimal('-123.456').abs().toString()
'123.456'

.floor()

Returns a new Decimal rounded down to the nearest integer.

>>> Decimal('123.456').floor().toString()
'123'
>>> Decimal('-123.456').floor().toString()
'-124'

.ceil()

Returns a new Decimal rounded up to the nearest integer.

>>> Decimal('123.456').ceil().toString()
'124'
>>> Decimal('-123.456').ceil().toString()
'-123'

.toFixed(decimals)

Returns a string representation of the decimal with a fixed number of decimal places. Rounds the last decimal place.

>>> Decimal('123.456').toFixed('2')
'123.46'
>>> Decimal('123').toFixed('2')
'123.00'

Static Methods

All instance methods are also available as static methods:

>>> Decimal.add('1.1', '2.2').toString()
'3.3'
>>> Decimal.abs('-123.456').toString()
'123.456'