stephenas / fincalc

Npm and Bower module to perform proper basic arithmetic operations with monetary values in JavaScript, or else two decimal precision arithmetic in a floating point scenario.

Fincalc

Introduction

Fincalc is a helper to perform proper basic arithmetic operations with monetary values in JavaScript, or else two decimal precision arithmetic in a floating point scenario. It also offers a utility to calculate the percentual variation between two values. It can be imported as a browser script on the front-end, or as an npm module on the back-end.

Install

Back-end

npm install fincalc

(add "--save" if you want the module to be automatically added to your project's "package.json" dependencies)

var fin = require(fincalc)

Front-end

bower install fincalc

(add "--save" if you want the module to be automatically added to your project's "bower.json" dependencies)

<script src="bower_components/fincalc/fincalc.js"></script>

(keep in mind this script will define an object "fin" that contains the methods described below, and might conflict if your scope contains another variable with the same name, or an object named "module" with a truthy "exports" key).

Why

The problem

Fincalc is made to fix a simple problem with JavaScript floating point operations.

Try this in your JavaScript console:

0.1 + 0.2 returns 0.30000000000000004

2.18 * 100 returns 218.00000000000003

The solution

fin(0.1 + 0.2) returns 0.3

fin(2.18 * 100) returns 218

API

Fincalc methods accept numbers (or string representation of them) as input, and return a single number rounded up to two decimal precision (i.e. to the money cent).

Rounding

fin(x)

Where x can be a number or an arithmetic operation:

fin(893.15784) // -> 893.16
fin(148.4528 + 9285.8864) // -> 9434.34
fin(2.18 * 200) // -> 436
fin(100 / 3) // -> 33.33

Calculate percentual variation

fin.pervar(x, y)

Returns the percentual variation between two values.

fin.pervar(456.12, 487.35) // -> 6.85
fin.pervar(23, 21) // -> -8.7

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MIT License