Decimalize

A JS decimal expressions library written in TypeScript

Allows you to write easily readable arithmetic expressions using more precise decimal types

const difference = (x, y) => dec`${x} - ${y}`;

Available from NPM

npm install decimalize

 

Numbers in JavaScript

Have you ever tried running 0.1 + 0.2 in your browser console?

If you have, you'll see that the answer is not 0.3 as you might expect, but instead 0.30000000000000004, this is due to inherent inaccuracy in how the IEEE 754 specification represents decimal numbers in binary (you can read more about this here).

For this reason, many languages offer some kind of decimal or precision type which trades speed and range for accuracy. These are useful for handling numbers where accuracy is more important, like financial applications.

JavaScript does not support any such type natively

 

While there are libraries available which can model decimal values more precisely, JavaScript also does not support operator overloading, which forces code to be written in method chains like:

a.add(b).dividedBy(c);

Even this simple example is not especially pretty to read, once you have a handful of these and then throw null or NaN into the mix, it starts to get pretty nasty.

 

Decimalize

This library uses Parzec in combination with BigNumber.js to deploy arithmetic expression parsing of precise decimals in the form of JS template literals

This means that instead of using method chains, you can write a simple, readable expression like

 dec`0.1 + 0.2` 

Here, the numbers will be parsed using the BigNumber.js library, rather than the JS native number type, so precision can be maintained

You can use variables as interpolated arguments in your expression

let price = dec`${cost} * ${tax}`;

You can also combine variables and static numbers in your expression

let result = dec`(${index} + 1) / ${base}`

const calculatePercentage = (amount, total) => dec`(${amount} / ${total}) * 100`

Argument Types

 

Arguments can be a number, string or BigNumber type, whatever values you pass in are immediately handed to the BigNumber constructor, and as such any invalid inputs will make the result of your expression the BigNumber representation of NaN (which can be coerced to native NaN as number type)

In future, this will be extended to allow you to configure how values such as NaN, null and undefined will be handled.

Operators

Decimalize currently supports the standard arithmetic operators, + * / - ( )

Additional operators may be added in future for exponents and other operations, but for now these are only supported by BigNumber in method syntax

Configuration

This library does not expose any configuration at the moment, however, there are various configuration options available for BigNumber.js, which you can read about over at its project page

Dependencies

The incredible BigNumber.js and the amazing Parzec, both of which are licensed under MIT, as is this library

Jasmine is also used for the test suite