Merge pull request #37 from evert/pow

POW operation.

.eslintrc.json

@@ -45,6 +45,7 @@
           "ts-expect-error": "allow-with-description"
         }
       ],
-      "@typescript-eslint/no-explicit-any" : 0
+      "@typescript-eslint/no-explicit-any" : 0,
+      "@typescript-eslint/no-this-alias": 0
   }
-}
+}

CHANGELOG.md

@@ -1,6 +1,12 @@
 Changelog
 =========
 
+1.2.0 (2020-08-01)
+------------------
+
+* Added `pow()` operation.
+
+
 1.1.1 (2020-02-02)
 ------------------
 

readme.md

@@ -118,6 +118,9 @@ const result = new Money(10).divide(3);
 
 // Multiplication
 const result = new Money('2000').multiply('1.25');
+
+// Powers
+const result = new Money(2).pow(8);
 ```
 
 ### Comparing objects

src/money.ts

@@ -110,6 +110,37 @@ export class Money {
 
   }
 
+  /**
+   * Pow returns the current value to it's exponent.
+   *
+   * pow currently only supports whole numbers.
+   */
+  pow(exponent: number | bigint): Money {
+
+    if (typeof exponent === 'number' && !Number.isInteger(exponent)) {
+      throw new Error('You can currently only use pow() with whole numbers');
+    }
+
+    if (exponent > 1) {
+      const resultBig = this.value ** BigInt(exponent);
+      return Money.fromSource(
+        divide(resultBig, PRECISION_M ** (BigInt(exponent)-1n), this.round),
+        this.currency,
+        this.round
+      );
+    } else {
+      // This handles the 0, 1 and negative exponent cases.
+      // This uses an iterative approach and is therefore not going to super
+      // fast.
+      let base:Money = this;
+      for(let i = 1; i > exponent; i--) {
+        base = base.divide(this);
+      }
+      return base;
+    }
+
+  }
+
   /**
    * Returns the absolute value.
    */

test/money.ts

@@ -287,6 +287,31 @@ describe('Money class', () => {
 
   });
 
+  describe('pow', () => {
+
+    const cases: [string|number, number, string][] = [
+      ['1',  5,'1.00'],
+      ['2',  8, '256.00'],
+      [5,    3, '125.00'],
+      [-10,  5, '-100000.00'],
+      [-10,  1, '-10.00'],
+      [-10,  0, '1.00'],
+      [2,   -2, '0.25'],
+    ];
+
+    for (const cas of cases) {
+
+      it(`${cas[0]} ** ${cas[1]} = ${cas[2]}`, () => {
+
+        const x = new Money(cas[0], 'CAD');
+        expect(x.pow(cas[1]).toFixed(2)).to.equal(cas[2]);
+
+      });
+
+    }
+
+  });
+
   describe('abs', () => {
 
     const cases = [