Money & Precision

Why Dinero.js

0.1 + 0.2 === 0.30000000000000004 in JavaScript — floating point arithmetic isn't safe for money. fx builds every calculation on Dinero.js, which represents money as an integer amount at a fixed scale (cents, not dollars-as-a-float) and only converts to a display string at the very end, via prettyPrint.

Base and exponent

Every currency fx supports is defined by its base (5 or 10) and exponent — how many minor units make one major unit, and in what numeral system:

interface CurrencyDefinition {
  code: string;
  base: 5 | 10;
  exponent: number;
}

Most currencies are base: 10 — 2 minor units of precision (100 cents per dollar). fx hand-rolls all 156 supported currencies from ISO 4217, rather than depending on a third-party currency-data package that could break the build.

Base-5 currencies

MGA (Malagasy ariary) and MRU (Mauritanian ouguiya) are base-5 currencies — their minor unit divides the major unit into 5ths, not 10ths:

CURRENCY_DATA.MGA; // { code: 'MGA', base: 5, exponent: 1 }
CURRENCY_DATA.MRU; // { code: 'MRU', base: 5, exponent: 1 }

Zero-decimal currencies

JPY (Japanese yen) and KRW (South Korean won) have no minor unit at all — exponent: 0:

CURRENCY_DATA.JPY; // { code: 'JPY', base: 10, exponent: 0 }
CURRENCY_DATA.KRW; // { code: 'KRW', base: 10, exponent: 0 }

Currencies fx deliberately excludes or re-adds

ILS (Israeli new shekel) is explicitly unsupported. STN (São Tomé and Príncipe dobra), SYP (Syrian pound), and ZWL (Zimbabwean dollar) — sometimes dropped by other currency-data sources — are explicitly included, each as a standard base-10, 2-decimal currency.