macor161 / ts-money

Typescript port of js-money. Implementation of the Money value object.

TS Money

TS Money is a Typescript port of the great js-money package, which is an implementation of Martin Fowlers Money pattern.

Install

npm install ts-money

Usage

First we need to import the library.

import { Money, Currencies } from 'ts-money'

or in javascript:

const TsMoney = require('ts-money')
const Money = TsMoney.Money
const Currencies = TsMoney.Currencies

Creating a new instance

There are multiple options of what to pass into the constructor to create a new Money instance:

• amount as number, currency as string
• amount as number, currency as object
• object with amount and currency fields (only with fromInteger and fromDecimal methods)

Amounts can be supplied either as integers or decimal numbers.

Instances of Money are immutable and each arithmetic operation will return a new instance of the object.

When using decimals the library will allow only decimals with the precision allowed by the currencies smallest unit.

const fiveEur = new Money(500, Currencies.EUR)
const tenDollars = Money.fromInteger({ amount: 1000, currency: Currencies.USD })
const someDollars = Money.fromDecimal(15.25, 'USD')

// the following will fail and throw an Error since USD allows for 2 decimals
const moreDollars = Money.fromDecimal(15.3456, Currencies.USD)
// but with rounder function provider the following will work
const someMoreDollars = Money.fromDecimal(15.12345, 'USD', Math.ceil)

The Currency interface hold the following properties:

interface Currency {
    symbol: string
    name: string
    symbol_native: string
    decimal_digits: number
    rounding: number
    code: string
    name_plural: string
}

Ex:

import { Currency } from 'ts-money'

const usd: Currency = {
    "symbol": "$",
    "name": "US Dollar",
    "symbol_native": "$",
    "decimal_digits": 2,
    "rounding": 0,
    "code": "USD",
    "name_plural": "US dollars"
}

Basic arithmetics

Arithmetic operations involving multiple objects are only possible on instances with the same currency and will throw an Error otherwise.

const fiveEur = new Money(500, Currencies.EUR) // 5 EUR

// add
fiveEur.add(new Money(250, Currencies.EUR)) // 7.50 EUR

// subtract 
fiveEur.subtract(new Money(470, Currencies.EUR)) // 0.30 EUR

// multiply
fiveEur.multiply(1.2345) // 6.17 EUR
fiveEur.multiply(1.2345, Math.ceil) // 6.18 EUR

// divide 
fiveEur.divide(2.3456) // 2.13 EUR
fiveEur.divide(2.3456, Math.ceil) // 2.14 EUR

Allocating funds

Will divide the funds based on the ratio without loosing any pennies.

const tenEur = new Money(1000, Currencies.EUR)

// divide 10 EUR into 3 parts
const shares = tenEur.allocate([1,1,1]) 
// returns an array of Money instances worth [334,333,333]

// split 5 EUR 70/30
const fiveEur = new Money(500, Currencies.EUR)
const shares = fiveEur.allocate([70,30])
// returns an array of money [350,150]

Comparison and equality

Two objects are equal when they are of the same amount and currency. Trying to compare 2 objects with different currencies will throw an Error.

const fiveEur = new Money(500, Currencies.EUR)
const anotherFiveEur = new Money(500, Currencies.EUR)
const sevenEur = new Money(700, Currencies.EUR)
const fiveDollars = new Money(500, Currencies.USD)

fiveEur.equals(fiveDollars) // return false
fiveEur.equals(anotherFiveEur) // return true

fiveEur.compare(sevenEur) // return -1
sevenEur.compare(fiveEur) // return 1
fiveEur.compare(anotherFiveEur) // return 0

fiveEur.compare(fileDollars) // throw Error

fiveEur.greaterThan(sevenEur) // return false
fiveEur.greaterThanOrEqual(sevenEur) // return false
fiveEur.lessThan(sevenEur) // return true
fiveEur.lessThanOrEqual(fiveEur) // return true

Modifications

Some changes have been made compared with the javascript version:

Currencies object

Currencies are now exported in a standalone object:

import { Money, Currencies } from 'ts-money'

Currencies.LTC = {
    symbol: "Ł",
    name: "Litecoin",
    symbol_native: "Ł",
    decimal_digits: 8,
    rounding: 0,
    code: "LTC",
    name_plural: "Litecoins"    
}

const m1 = new Money(12, 'LTC')
const m2 = new Money(234, Currencies.USD)
const m3 = new Money(543, Currencies.LTC)

Case insensitive currencies

Money accepts currencies as case insensitive:

const m1 = new Money(1, 'usd')
const m2 = new Money(2, 'USD')
const m3 = new Money(3, 'Usd')

Development

Install dependencies

npm install

Build library

npm run build

Run tests

npm test

🎁 Thank you for your donations

TS Money is an open source library and is completely free to use.

If you find this project useful and would like to support its development, consider making a donation.

License

The MIT License

ts-money's Issues

Operations not working

Hello,

Looks like this package does not work when respecting the doc examples

Not working code:

 const fiveEur = new Money(500, Currencies.EUR); // 5 EUR
 // add
 fiveEur.add(new Money(250, Currencies.EUR)); // 7.50 EUR

console.log(fiveEur);

Money { amount: 500, currency: 'EUR' }

Looks like 250 was not added

Working code:

 const fiveEur = new Money(500, Currencies.EUR).add(new Money(250, Currencies.EUR));

console.log(fiveEur);

Money { amount: 7500, currency: 'EUR' }

Why ECMAScript target version is ES6 but not ES5?

IE doesn't support ES6 syntax, so I need to transpile ts-money module to ES5, seems to be better change target version to ES5 here to avoid similar problems.

Typo in README.md

nit: Replace "loosing" with "losing".

INR using Rs instead of ₹ as symbol

Why is the INR using Rs as symbol when the sign of the rupee seems to be ₹?

ts-money/lib/currencies.ts

Line 446 in 9ed1091

"symbol": "Rs",

Money.fromDecimal is subject to floating point calculation errors

These lines are subject to floating point errors:

let precisionMultiplier = Math.pow(10, currency.decimal_digits)
let resultAmount = amount * precisionMultiplier

For example:

The result of this calculation is assumed to be an integer:

if (!isInt(amount))
    throw new TypeError('Amount must be an integer')

but because of floating point calculation inaccuracies that's not always the case.

It's easy to workaround this issue by passing a rounder to Math.fromDecimal, but I feel like this issue is better fixed by ts-money itself, e.g. by using a default rounder.

Would you be open to a PR to address this?