javascriptclass/loan.html at main · zachlucas1/javascriptclass · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Loan Calculator</title>
    <script>
        function doPayment(){
            //input
            let principal = parseFloat(document.getElementById('principal').value);
            let annualRate = parseFloat(document.getElementById('annualRate').value);
            let years = parseFloat(document.getElementById('years').value);
            let paymentsPerYear = parseFloat(document.getElementById('paymentsPerYear').value);

            //output
            document.getElementById('outputPayment').innerHTML = `$${computePayment(principal, annualRate, years, paymentsPerYear)}`;
        }

        function doBalance() {
            //input
            let principal = parseFloat(document.getElementById('principal').value);
            let annualRate = parseFloat(document.getElementById('annualRate').value);
            let years = parseFloat(document.getElementById('years').value);
            let paymentsPerYear = parseFloat(document.getElementById('paymentsPerYear').value);
            let numberOfPaymentPaidToDate = parseFloat(document.getElementById('numberOfPaymentPaidToDate').value);

            //output
            document.getElementById('outputBalance').innerHTML = `$${computeBalance(principal, annualRate, years, paymentsPerYear, numberOfPaymentPaidToDate)}`;
        }

        function computePayment(principal, annualRate, years, paymentsPerYear){
            //variables / math
            let r = annualRate / paymentsPerYear;
            let n = -1 * (years * paymentsPerYear)

            //math
            let p = ((principal * r) / [1 - (1 + r) **n]).toFixed(2);

            //output
            return p;
        }

        function computeBalance(principal, annualRate, years, paymentsPerYear, numberOfPaymentPaidToDate) {
            //variables / math
            let r = annualRate / paymentsPerYear;
            let n = paymentsPerYear * years;
            let payment = computePayment(principal, annualRate, years, paymentsPerYear);

            //math
            let p = ([principal * ((1 + r) **numberOfPaymentPaidToDate)] - payment *(((1 + r) **numberOfPaymentPaidToDate) - 1) / r).toFixed(2);

            //output
            return p;
        }
    </script>
</head>
<body>
    <h1>Loan Calculator</h1>
    Amount borrowed (principal): <input id="principal">
    <br>
    Annual interest rate (example .08): <input id="annualRate">
    <br>
    Number of years: <input id="years">
    <br>
    Payments per year: <input id="paymentsPerYear">
    <br>
    <button type="button" onclick="doPayment()">Compute payment</button>
    <div id="outputPayment"></div>
    Number of Payments paid to date: <input id="numberOfPaymentPaidToDate">
    <br>
    <button type="button" onclick="doBalance()">Compute payoff amount</button>
    <div id="outputBalance"></div>
</body>
</html>