THE CODE FOR: LOAN SHARK

                        
                            // Get the loan information from the page.
function getValues() {

    // Step 1: Get values from the page.
    let loanAmount = Number(document.getElementById("loanAmount").value);
    let loanTerms = parseInt(document.getElementById("loanTerms").value);
    let loanRate = parseFloat(document.getElementById("loanRate").value);

    // Check for NaN
    if (isNaN(loanAmount)) {
        alert("Enter a valid loan amount. Must be a number.");
        document.getElementById("loanAmount").focus();
    } else if (isNaN(loanTerms)) {
        alert("Enter valid payment terms. Must be entered in number of months.");
        document.getElementById("loanTerms").focus();
    } else if (isNaN(loanRate)) {
        alert("Enter a valid interest rate. Leave off any symbols.");
        document.getElementById("loanRate").focus();
    } else {

        // Convert annual rate to monthly rate
        let monthlyRate = calcRate(loanRate);

        // Calculate monthly payment
        let loanPayment = calcPayment(loanAmount, monthlyRate, loanTerms);

        // Build schedule
        let payments = buildSchedule(loanAmount, monthlyRate, loanTerms, loanPayment);

        displayData(payments, loanAmount, loanPayment);
    }

}

// Builds an amortization schedule.
function buildSchedule(amount, rate, term, payment) {

    let payments = [];

    let balance = amount;
    let totalInterest = 0;
    let monthlyInterest = 0;
    let monthlyPrincipal = 0;

    for (let month = 1; month <= term; month++) {

        monthlyInterest = calcInterest(balance, rate);
        totalInterest += monthlyInterest;
        monthlyPrincipal = payment - monthlyInterest;
        balance = balance - monthlyPrincipal;

        let currentPayment = {
            month: month,
            payment: payment,
            principal: monthlyPrincipal,
            interest: monthlyInterest,
            totalInterest: totalInterest,
            balance: balance
        }

        payments.push(currentPayment);

    }

    return payments;

}

// Display table of payments.
// Display summary information at the top of the page.
function displayData(payments, loanAmount, payment) {

    let tableBody = document.getElementById("scheduleBody");
    let template = document.getElementById("scheduleTemplate");

    // Clear the table of previous values
    tableBody.innerHTML = "";

    for (let index = 0; index < payments.length; index++) {

        // Clone the template
        paymentRow = document.importNode(template.content, true);

        // Get the array of columns
        paymentCols = paymentRow.querySelectorAll("td");

        paymentCols[0].textContent = payments[index].month;
        paymentCols[1].textContent = payments[index].payment.toFixed(2);
        paymentCols[2].textContent = payments[index].principal.toFixed(2);
        paymentCols[3].textContent = payments[index].interest.toFixed(2);
        paymentCols[4].textContent = payments[index].totalInterest.toFixed(2);
        paymentCols[5].textContent = payments[index].balance.toFixed(2);

        // Write the payment to the page
        tableBody.appendChild(paymentRow);


    }

}

// Calculates a payment / rate is a monthly rate, term is total-months
function calcPayment(amount, rate, term) {
    let payment = 0;
    payment = (amount * rate) / (1 - Math.pow(1 + rate, -term));
    return payment;
}

// Calculates monthly rate for loan duration.
function calcRate(rate) {
    return rate = rate / 1200;
}

// Current balance and monthly rate
function calcInterest(balance, rate) {
    return balance * rate;
}
                        
                    

Loan Shark is based in multiple functions:

"Gets" the values input by the user (loan amount, lnegth of loan, and interest rate).

Validates whether or not the information is permissible (no incorrect symbols, words vs numbers, etc).

Builds an amortization schedule (listing individual components such as monthly and total interest, remaining balance, payment, etc).

Creates an array to pull information from our template to plug into our display table.

Displays our payment, loan length, principal, interest paid, total interest, and total balance remaining.