Decimal.js

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'