The Code for Loan Shark.
//Get info from the user. Calculate Results
let cPayments = parseFloat(months.value);
function getValues(){
console.log('Calculating...');
// Form variables
let amount = document.getElementById('amount');
let interest = document.getElementById('interest');
let months = document.getElementById('months');
// parse the numbers
let principal = parseFloat(amount.value);
let cInterest = parseFloat(interest.value) / 100/ 12;
let cPayments = parseFloat(months.value);
//Compute monthly payment with calculate function - Casey Spaulding
calculate(principal, cPayments, cInterest)
}
function calculate(principal, cPayments, cInterest){
//Compute monthly payment, interest, etc
let x = Math.pow(1+cInterest, cPayments);
let monthly = (principal * x * cInterest)/(x-1);
let total_payments = (monthly * cPayments).toFixed(2);
let total_interest_sum = ((monthly * cPayments)-principal).toFixed(2);
let formatCurrency = new Intl.NumberFormat(undefined, {
style: 'currency',
currency: 'USD'
});
let fmonthly = formatCurrency.format(monthly);
let fprincipal = formatCurrency.format(principal);
let ftotal_payments = formatCurrency.format(total_payments);
let ftotal_interest_sum = formatCurrency.format(total_interest_sum);
let info="";
info += "";
info += "Monthly Payment:
"+fmonthly+"
Loan Amount: ";
info += ""+fprincipal+" Total Payments: ";
info += ""+ftotal_payments+" Total Interest Paid: ";
info += ""+ftotal_interest_sum+" Payments: ";
info += ""+cPayments+"
";
//info is a string containing all the html table code
document.getElementById("loan_info").innerHTML = info;
// TABLE DATA
let table="";
table += "";
table += "";
table += " Month ";
table += "Payment ";
table += "Principle ";
table += " Interest ";
table += "Interest Paid ";
table += "Balance ";
table += " ";
let current_balance = parseFloat(document.getElementById('amount').value);
let interest = parseFloat(document.getElementById('interest').value);
let monthly_payment = monthly
let payment_counter = 1;
let total_interest = parseFloat(cInterest);
while (payment_counter <= cPayments) {
towards_interest = cInterest * current_balance;
towards_balance = monthly_payment - towards_interest;
total_interest = total_interest + towards_interest;
current_balance = current_balance - towards_balance;
let ftowards_interest = formatCurrency.format(towards_interest);
let ftowards_balance = formatCurrency.format(towards_balance);
let ftotal_interest = formatCurrency.format(total_interest);
let fcurrent_balance = formatCurrency.format(current_balance);
let fmonthly_payment = formatCurrency.format(monthly_payment);
table += "";
table += ""+payment_counter+" "
table += ""+fmonthly_payment+" "
table += ""+ftowards_balance+" "
table += ""+ftowards_interest+" "
table += ""+ftotal_interest+" "
table += ""+fcurrent_balance+" "
table += " ";
payment_counter++;
}
table +="
";
document.getElementById("tablehtml").innerHTML = table;
}
function round(num, dec){
return (Math.round(num*Math.pow(10,dec))/ Math.pow(10,dec)).toFixed(dec);
}
// Show Error
function showError(error){
// Creat a div
const errorDiv = document.createElement('div');
// Get elements
const card = document.querySelector('.card');
const heading = document.querySelector('.heading');
// Add class
errorDiv.className = 'alert alert-danger';
// Create text node and append to div
errorDiv.appendChild(document.createTextNode(error));
// Insert error above heading
card.insertBefore(errorDiv, heading);
// Clear error after 3 seconds
setTimeout(clearError, 3000);
}
The Code is structured in two functions.
GetValues Function
GetValues is a function that gathers all the data from the page and validates it. Then sends it to the calculate function
Calculate Function
Calculate is a function that calculates the monthly payments, interest, etc and then displays a summary and an amortization table for the user. I used the formatCurrency.format(total_interest_sum) for the amounts.