Remove duplication between Dollar and Franc

src/dollar/index.ts

@@ -1,15 +1,11 @@
-export default class Dollar {
-  private amount: number;
+import Money from '../money';
 
+export default class Dollar extends Money {
   constructor(amount: number) {
-    this.amount = amount;
+    super(amount);
   }
 
   times(multiplier: number): Dollar {
     return new Dollar(this.amount * multiplier);
   }
-
-  equals(dollar: Object): boolean {
-    return this.amount == (dollar as Dollar).amount;
-  }
 }

src/franc/index.spec.ts

@@ -1,4 +1,5 @@
 import Franc from '.';
+import Dollar from '../dollar';
 
 describe('Franc', () => {
   describe('multiplication', () => {
@@ -16,4 +17,13 @@ describe('Franc', () => {
       expect(product.equals(new Franc(15))).toBe(true);
     });
   });
+
+  describe('equality', () => {
+    it('should consider an object representing $5 equals to another object representing $5', () => {
+      expect(new Franc(5).equals(new Franc(5))).toBe(true);
+      expect(new Franc(5).equals(new Franc(6))).toBe(false);
+      expect(new Dollar(5).equals(new Dollar(5))).toBe(true);
+      expect(new Dollar(5).equals(new Dollar(6))).toBe(false);
+    });
+  });
 });

src/franc/index.ts

@@ -1,15 +1,11 @@
-export default class Franc {
-  private amount: number;
+import Money from '../money';
 
+export default class Franc extends Money {
   constructor(amount: number) {
-    this.amount = amount;
+    super(amount);
   }
 
   times(multiplier: number): Franc {
     return new Franc(this.amount * multiplier);
   }
-
-  equals(dollar: Object): boolean {
-    return this.amount == (dollar as Franc).amount;
-  }
 }

src/money/index.ts

@@ -0,0 +1,16 @@
+export default class Money {
+  private _amount: number;
+
+  constructor(amount: number) {
+    this._amount = amount;
+  }
+
+  get amount() {
+    return this._amount;
+  }
+
+  equals(obj: Object): boolean {
+    const money: Money = obj as Money;
+    return this.amount == money.amount;
+  }
+}