improve example

Author: jessealama

examples/mortgage.ts

@@ -4,18 +4,28 @@ import { pow } from "./pow.mjs";
 const one = new Decimal128("1");
 const paymentsPerYear = new Decimal128("12");
 
-function calculateMonthlyPayment(p: string, r: string, y: string): Decimal128 {
-    const principal = new Decimal128(p);
-    const annualInterestRate = new Decimal128(r);
-    const years = new Decimal128(y);
+function calculateMonthlyPayment(
+    principal: Decimal128,
+    annualInterestRate: Decimal128,
+    years: Decimal128
+): Decimal128 {
     const monthlyInterestRate = annualInterestRate.divide(paymentsPerYear);
     const paymentCount = paymentsPerYear.multiply(years);
     const onePlusInterestRate = monthlyInterestRate.add(one);
-    const ratePower = pow(onePlusInterestRate, Number(paymentCount));
-
-    const x = principal.multiply(monthlyInterestRate);
-
-    return x.multiply(ratePower).divide(ratePower.subtract(one));
+    const ratePower = pow(
+        onePlusInterestRate,
+        Number(paymentCount.toString({ numDecimalDigits: 0 }))
+    );
+    return principal
+        .multiply(monthlyInterestRate)
+        .multiply(ratePower)
+        .divide(ratePower.subtract(one));
 }
 
-console.log(calculateMonthlyPayment("5000000", "0.05", "30").toString());
+console.log(
+    calculateMonthlyPayment(
+        new Decimal128("5000000"),
+        new Decimal128("0.05"),
+        new Decimal128("30")
+    ).toString({ numDecimalDigits: 2 })
+);