The Code

                
// clear the table before displaying new results
function clearTable() {
  const dataTable = document.getElementById("monthlyData");
  while (dataTable.firstChild) {
    dataTable.removeChild(dataTable.firstChild);
  }
}

// get the values for the loan out of the form
// validate inputs
function getValues() {
  let loanAmount = parseFloat(document.getElementById("loanAmount").value);
  let loanTerm = parseInt(document.getElementById("loanTerm").value);
  let interestRate = parseFloat(document.getElementById("interestRate").value);

  document.getElementById("monthlyPayment").innerText = "$0.00";

  if (
    !isNaN(loanAmount) &&
    !isNaN(loanTerm) &&
    !isNaN(interestRate) &&
    loanAmount > 0 &&
    loanTerm > 0 &&
    interestRate > 0
  ) {
    clearTable(); // clear the table before displaying new results
    let totals = calculateTotals(loanAmount, loanTerm, interestRate);
    let payments = calculatePayments(loanAmount, loanTerm, interestRate);

    calculatePayments(loanAmount, loanTerm, interestRate);
    displayTotals(totals);
    displayPayments(payments);
  } else {
    Swal.fire({
      icon: "error",
      backdrop: false,
      title: "Uh oh!",
      text: "Please enter valid numbers for your loan details.",
    });
  }
}

// calculate the loan payments

// calculate the totals
function calculateTotals(loanAmount, loanTerm, interestRate) {
  // get the monthly payment
  let monthlyPayment = calculateMonthlyPayment(
    loanAmount,
    loanTerm,
    interestRate
  );
  // total cost is monthly payment * loanTerm
  let totalCost = monthlyPayment * loanTerm;
  // total interest is cost - principal
  let totalInterest = totalCost - loanAmount;

  let totals = {
    monthlyPayment: monthlyPayment,
    loanAmount: loanAmount,
    interest: totalInterest,
    cost: totalCost,
  };

  return totals;
}
// calculate the amortization schedule
function calculatePayments(loanAmount, loanTerm, interestRate) {
  // get the monthly payment
  let monthlyPayment = calculateMonthlyPayment(
    loanAmount,
    loanTerm,
    interestRate
  );
  // calculate the remaining values
  let balance = loanAmount;
  let totalInterest = 0;

  let payments = [];

  for (let month = 1; month <= loanTerm; month++) {
    let interest = balance * (interestRate / 1200);
    let principalPayment = monthlyPayment - interest;
    totalInterest += interest;
    balance -= principalPayment;

    let loanPayment = {
      month: month,
      payment: monthlyPayment,
      principal: principalPayment,
      interest: interest,
      totalInterest: totalInterest,
      balance: Math.abs(balance),
    };

    payments.push(loanPayment);
  }

  return payments;
}

function calculateMonthlyPayment(loanAmount, loanTerm, interestRate) {
  let monthlyPayment =
    (loanAmount * (interestRate / 1200)) /
    (1 - (1 + interestRate / 1200) ** -loanTerm);

  return monthlyPayment;
}

// disply calculations on the page

// display totals
function displayTotals(loanTotals) {
  let formatter = new Intl.NumberFormat("en-US", {
    style: "currency",
    currency: "USD",
  });

  document.getElementById("monthlyPayment").innerText = formatter.format(
    loanTotals.monthlyPayment
  );
  document.getElementById("totalPrincipal").innerText = formatter.format(
    loanTotals.loanAmount
  );
  document.getElementById("totalInterest").innerText = formatter.format(
    loanTotals.interest
  );
  document.getElementById("totalCost").innerText = formatter.format(
    loanTotals.cost
  );
}

// display table rows
function displayPayments(loanPayments) {
  const dataTable = document.getElementById("monthlyData");
  const template = document.getElementById("tableRowTemplate");

  let formatter = new Intl.NumberFormat("en-US", {
    style: "currency",
    currency: "USD",
  });

  for (let i = 0; i < loanPayments.length; i++) {
    let payment = loanPayments[i];

    let tableRow = document.importNode(template.content, true);
    let tds = tableRow.querySelectorAll("td");

    tds[0].textContent = payment.month;
    tds[1].textContent = formatter.format(payment.payment);
    tds[2].textContent = formatter.format(payment.principal);
    tds[3].textContent = formatter.format(payment.interest);
    tds[4].textContent = formatter.format(payment.totalInterest);
    tds[5].textContent = formatter.format(payment.balance);

    dataTable.appendChild(tableRow);
  }
}

                
            

clearTable

This function clears the contents of a table with the id "monthlyData" by removing all its child elements.

getValues

This function retrieves the values entered in a loan form, validates the inputs, and proceeds with calculations and display if the inputs are valid. Otherwise, it shows an error message using the Swal.fire library.

calculateTotals

This function calculates the total cost, total interest, and monthly payment for a loan based on the provided loan amount, loan term (in months), and interest rate. It returns an object containing these calculated values.

calculatePayments

This function calculates the amortization schedule for a loan based on the loan amount, loan term, and interest rate. It iterates over the loan term and calculates the principal, interest, total interest, and remaining balance for each month. It returns an array of objects representing each payment month's details.

calculateMonthlyPayment

This function computes the monthly payment amount for a loan based on the loan amount, loan term (in months), and interest rate. It uses the formula for calculating the monthly payment.

displayTotals

This function takes the loan totals object and displays the monthly payment, total principal, total interest, and total cost on the page. It formats the values as currency using the Intl.NumberFormat object.

displayPayments

This function takes the array of loan payments and displays them in a table on the page. It iterates over each payment object, formats the values as currency, and appends a table row to the "monthlyData" table for each payment.

These functions work together to clear the table, retrieve and validate loan details, perform calculations, and display the results on the page for a loan amortization calculator.