add ability to add two money of different currencies

Author: lykmapipo

lib/money.js

@@ -16,6 +16,8 @@ var BigDecimal = require('big.js');
  * @public
  */
 function Money(amount, currency, time) {
+    //TODO add ability to instantiate money with varargs
+
     //set a date when this money has been created
     //Note!: Money value flactuate with time
     //
@@ -171,13 +173,31 @@ Money.prototype.divide = Money.prototype.divideBy = function(divisor) {
  * @returns {Money} a new money instance which hold the result of operation
  */
 Money.prototype.add =
-    Money.prototype.plus = function(other) {
-        //check if they have same currency
-        if (_.isEqual(this.currency, other.currency)) {
-            return new Money(this.amount.plus(other.amount), this.currency);
-        } else {
-            //TODO handle diffent currency
-            return this;
+    Money.prototype.plus = function(other, done) {
+        //this is of money instance context
+        var self = this;
+
+        //other money instance has the same
+        //currency as this money instance
+        if (_.isEqual(self.currency, other.currency)) {
+            done(null, new Money(self.amount.plus(other.amount), self.currency));
+        }
+
+        //other have differnt currency to this
+        //money instance
+        else {
+            async.waterfall([
+                function convertOtherToThisMoneyCurrency(next) {
+                    other.convertTo(self.currency, next);
+                },
+                function sum(exchanged, next) {
+                    next(null,
+                        new Money(
+                            self.amount.plus(exchanged.amount),
+                            self.currency)
+                    );
+                }
+            ], done);
         }
     };
 
@@ -192,14 +212,33 @@ Money.prototype.add =
  * @private
  */
 Money.prototype.subtract =
-    Money.prototype.minus = function(other) {
-        //check if they have same currency
-        if (_.isEqual(this.currency, other.currency)) {
-            return new Money(this.amount.minus(other.amount), this.currency);
-        } else {
-            //TODO handle diffent currency
-            return this;
+    Money.prototype.minus = function(other, done) {
+        //this if of money instance context
+        var self = this;
+
+        //other money instance has the same
+        //currency as this money instance
+        if (_.isEqual(self.currency, other.currency)) {
+            done(null, new Money(self.amount.minus(other.amount), self.currency));
         }
+
+        //other have differnt currency to this
+        //money instance
+        else {
+            async.waterfall([
+                function convertOtherToThisMoneyCurrency(next) {
+                    other.convertTo(self.currency, next);
+                },
+                function subtract(exchanged, next) {
+                    next(null,
+                        new Money(
+                            self.amount.minus(exchanged.amount),
+                            self.currency)
+                    );
+                }
+            ], done);
+        }
+
     };
 
 

moneyjs.png

@@ -1,9 +1,10 @@
 {
-    "name": "MoneyJS",
+    "name": "moneyjs",
     "version": "0.1.0",
     "description": "Nodejs library to represent monetary amounts",
     "keywords": [
         "money",
+        "monetary",
         "currency",
         "convert",
         "coin",

package.json

@@ -101,24 +101,27 @@ describe('Money', function() {
         it('should be able to perform addition on two money instance of the same currency', function(done) {
             var price = new Money(12, Money.USD);
             var tax = new Money(2, Money.USD);
-            var priceAfterTax = price.plus(tax);
+            price.plus(tax, function(error, priceAfterTax) {
 
-            expect(priceAfterTax.amount.toString()).to.be.equal('14');
-            expect(price.currency.code).to.be.equal('USD');
+                expect(priceAfterTax.amount.toString()).to.be.equal('14');
+                expect(price.currency.code).to.be.equal('USD');
 
-            done();
+                done(error, priceAfterTax);
+            });
 
         });
 
+
         it('should be able to perform subtraction on two money instance of the same currency', function(done) {
-            var price = new Money(12, Money.USD);
+            var profit = new Money(12, Money.USD);
             var tax = new Money(2, Money.USD);
-            var netProfit = price.minus(tax);
+            profit.minus(tax, function(error, netProfit) {
 
-            expect(netProfit.amount.toString()).to.be.equal('10');
-            expect(netProfit.currency.code).to.be.equal('USD');
+                expect(netProfit.amount.toString()).to.be.equal('10');
+                expect(netProfit.currency.code).to.be.equal('USD');
 
-            done();
+                done(error, netProfit);
+            });
 
         });
     });
@@ -304,6 +307,40 @@ describe('Money', function() {
 
         });
 
+
+        it('should be able to perform addition on two money instance of the different currency', function(done) {
+            var price = new Money(1, Money.KES);
+            var tax = new Money(1800, Money.TZS);
+            price.plus(tax, function(error, priceAfterTax) {
+
+                expect(error).to.be.null;
+                expect(priceAfterTax).to.not.be.null;
+
+                expect(priceAfterTax.amount.toString()).to.be.equal('91');
+                expect(price.currency.code).to.be.equal('KES');
+
+                done(error, priceAfterTax);
+            });
+
+        });
+
+
+        it('should be able to perform subtraction on two money instance of the different currency', function(done) {
+            var profit = new Money(950, Money.KES);
+            var tax = new Money(1800, Money.TZS);
+            profit.minus(tax, function(error, netProfit) {
+
+                expect(error).to.be.null;
+                expect(netProfit).to.not.be.null;
+
+                expect(netProfit.amount.toString()).to.be.equal('860');
+                expect(netProfit.currency.code).to.be.equal('KES');
+
+                done(error, netProfit);
+            });
+
+        });
+
     });