fix(fractionless): honor decimals in fractionless amounts (#265)

Honor the configured precision, as defined by `options.decimals` or
`currency` if `options.decimals = undefined`, when instatiating with
`.fromFractionlessAmount()` and converting `.toFractionlessAmount()`.

Fixes old behavior:
```
Money.fromFractionlessAmount(1000, 'NOK', { decimals: 3 }) => 10.000 NOK
money.toFractionlessAmount() => 1000 NOK
```
To expected behavior:
```
Money.fromFractionlessAmount(1000, 'NOK', { decimals: 3 }) => 1.000 NOK
money.toFractionlessAmount() => 1000 NOK
```

README.md

@@ -233,6 +233,8 @@ export declare class Money {
      *
      * Example:
      * Money.fromFractionlessAmount(1000, 'NOK') => 10.00 NOK
+     * Money.fromFractionlessAmount(1000, 'NOK', { decimals: 2 }) => 10.00 NOK
+     * Money.fromFractionlessAmount(1000, 'NOK', { decimals: 3 }) => 1.000 NOK
      */
     static fromFractionlessAmount(
         amount: number,
@@ -314,7 +316,8 @@ export declare class Money {
 
     // Converters
     /**
-     * Converts the money amount into a whole number given in the minor unit of the currency
+     * Converts the money amount into a whole number given in the minor unit of the currency.
+     * Honors the current precision in use.
      */
     toFractionlessAmount: () => number;
     /**

src/__tests__/money.test.ts

@@ -152,6 +152,32 @@ describe("money", () => {
         expect(result).toBe("10.00");
     });
 
+    it("should instantiate from fractionless amount and honor decimals in options", () => {
+        const result = Money.fromFractionlessAmount(1000, "NOK", {
+            decimals: 3,
+        }).toString();
+        expect(result).toBe("1.000");
+    });
+
+    it("should convert to fractionless amount", () => {
+        const result = Money.of(10, "NOK").toFractionlessAmount();
+        expect(result).toBe(1000);
+    });
+
+    it("should convert from fractionless amount to fractionless amount and honor decimals in options", () => {
+        const result = Money.fromFractionlessAmount(1000, "NOK", {
+            decimals: 3,
+        }).toFractionlessAmount();
+        expect(result).toBe(1000);
+    });
+
+    it("should convert from normal to fractionless amount and honor decimals in options", () => {
+        const result = Money.of(10, "NOK", {
+            decimals: 4,
+        }).toFractionlessAmount();
+        expect(result).toBe(100000);
+    });
+
     it("should print in locale", () => {
         const result = Money.of(5.5, "NOK").toLocaleString("no-NB");
         expect(result).toBe("5,50");

src/index.ts

@@ -146,15 +146,16 @@ export class Money {
      *
      * Example:
      * Money.fromFractionlessAmount(1000, 'NOK') => 10.00 NOK
+     * Money.fromFractionlessAmount(1000, 'NOK', { decimals: 2 }) => 10.00 NOK
+     * Money.fromFractionlessAmount(1000, 'NOK', { decimals: 3 }) => 1.000 NOK
      */
     static fromFractionlessAmount(
         amount: number,
         currency: string,
         options?: AdditionalOptions,
     ): Money {
-        return Money.of(amount, currency, options).divide(
-            10 ** currencyToDecimals(currency),
-        );
+        const decimals = options?.decimals ?? currencyToDecimals(currency);
+        return Money.of(amount, currency, options).divide(10 ** decimals);
     }
 
     /**
@@ -309,10 +310,13 @@ export class Money {
     };
 
     /**
-     * Converts the money amount into a whole number given in the minor unit of the currency
+     * Converts the money amount into a whole number given in the minor unit of the currency.
+     * Honors the current precision in use.
      */
     toFractionlessAmount = (): number => {
-        return this.multiply(10 ** currencyToDecimals(this.currency()))
+        const decimals =
+            this.getDecimals() ?? currencyToDecimals(this.currency());
+        return this.multiply(10 ** decimals)
             .round(0)
             .toNumber();
     };