Change.js

Change.js is about the simplest you can get with money calculations for USD. Initialize a Change object with dollars or cents and add or subtract amounts or calculate tax. All calculations are done in cents to avoid floating point errors. All operations return the result in a new instance of Change.

Currency formatting and rounding can be customized via dependency injection.

Setup

Requiring

Change exports a function to support injecting dependencies as arguments. When you don't want to customize anything, this just means you'll need to call it without arguments upon requiring:

var Change = require('change-js')();

Injecting dependencies

You can control how money is formatted and how decimals are rounded. For formatting, see formatMoney in accounting.js.

var Change = require('change-js')({
  formatter: accounting.formatMoney,
  rounder: Math.floor
});

Usage

Initializing

// With cents
var c2 = new Change({ cents: 1050 });
 
// With dollars
var c1 = new Change({ dollars: 10.5 });

Calculations

All calculations return new Change instances and do not mutate the original object.

var sum = c1.add(c2);
var difference = c1.subtract(c2);
 
var total = sum.multiply(2);
var discounted = sum.multiply(0.25);
 
// With a percentage, for convenience
var tax = sum.multiplyPercent(8.25);
 
// Chaining
var total = c1.add(c2).multiplyPercent(8.25);

Getting your dollars back!

// As a float
sum.dollars();
 
// As formatted US dollars (requires injecting a formatter)
sum.formattedDollars();

Caveats

Change.js currently only supports US dollars.