การคำนวณเงินด้วยจำนวนเต็ม

if (a.currency !== b.currency) throw new Error("currency");
if (![a.minor, b.minor].every(Number.isSafeInteger)) throw new Error("amount");
const minor = a.minor + b.minor;
if (!Number.isSafeInteger(minor)) throw new Error("range");
return { currency: a.currency, minor };