//Helper Functions
                            let $ = function(id){
                                return document.getElementById(id);
                            }
                            
                            let USD = function(num){
                                return num.toLocaleString('en-US', {style: 'currency', currency: 'USD'});
                            }
                            
                            /**
                             * Controller Function
                             * Gather form data
                             */
                            function gatherInput(){
                            
                                //User Input
                                let loanAmount       = parseInt($('inputLoanAmount').value);   //Principal Amount
                                let numberOfPayments = parseInt($('inputLoanPayments').value); //Number of Months
                                let loanRate         = parseInt($('inputLoanRate').value);     //Interest Rate
                            
                                //array of result objects for each individual month
                                let statements = [];
                            
                                //Validation
                                if (Number.isInteger(loanAmount) && Number.isInteger(numberOfPayments) 
                                    && Number.isInteger(loanRate)){
                            
                                        //generate statements array containg an object for each month
                                        let statements = generateReport(loanAmount, numberOfPayments, loanRate);
                            
                                        //View function
                                        displayResults(statements);
                            
                                    } else alert('Invalid Input');
                            }
                            
                            /**
                             * Logic Functions
                             * Calculate prices and rates, then return a array of objects 
                             * containing payment statemens for each month
                             */
                            function generateReport(loanAmount, numberOfPayments, interestRate){
                            
                                //Results array used to contain statements for each individual month
                                let monthlyStatements = [];
                            
                                //Used in for loop to determine previous statement's balance
                                let previousRemainingBalance = loanAmount;
                            
                                for (let index = 0; index < numberOfPayments; index++) {
                                    //Statement object used for holding calculation results for current idividual month
                                    let statement = {};
                            
                                    //Feeding calculations into statement object 
                                    statement.totalMonthlyPayment = (loanAmount) * (interestRate/1200) / (1 - (1 + interestRate/1200)**(-Math.abs(numberOfPayments)));
                                    statement.interestPayment = previousRemainingBalance * (interestRate/1200)
                                    statement.principalPayment = statement.totalMonthlyPayment - statement.interestPayment;
                                    statement.remainingBalance = previousRemainingBalance - statement.principalPayment;
                            
                                    //Push results into monthly statements array
                                    monthlyStatements.push(statement);
                            
                                    //Adjust previous payment for the next iteration
                                    previousRemainingBalance = statement.remainingBalance;
                                }
                            
                                return monthlyStatements;
                            }
                            
                            
                            /**
                             * View Functio
                             * Post overview results + detail table
                             */
                            function displayResults(statements){
                            
                                //Gather HTML
                                let tableBody    = $('tableResults');
                                let templateHead = $('headTemplate');
                                let templateRow  = $('rowTemplate');
                            
                                //Clear HTML
                                tableBody.innerHTML = '';
                            
                                //Generate total amounts
                                let totalPrincipal = 0;
                                let totalInterest  = 0;
                            
                                for (let index = 0; index < statements.length; index++) {
                                    totalPrincipal += statements[index].principalPayment;
                                    totalInterest += statements[index].interestPayment;
                                }
                            
                                let totalCost = totalPrincipal + totalInterest;
                            
                                //Convert results to currency and display on page
                                $('totalMonthlyPayment').innerHTML  = USD(statements[0].totalMonthlyPayment);
                                $('totalPrincipalResult').innerHTML = USD(totalPrincipal);
                                $('totalInterestResult').innerHTML  = USD(totalInterest);
                                $('totalCostResult').innerHTML      = USD(totalCost);
                            
                                //Generate table head 
                                let tableHead = document.importNode(templateHead.content, true);
                                let headCols = tableHead.querySelectorAll("th");
                            
                                headCols[0].textContent = 'Month';
                                headCols[1].textContent = 'Payment';
                                headCols[2].textContent = 'Principal';
                                headCols[3].textContent = 'Interest';
                                headCols[4].textContent = 'Total Interest';
                                headCols[5].textContent = 'Balance';
                            
                                tableBody.appendChild(tableHead);
                            
                                //Generate table Body
                                tableBody.innerHTML += "<tbody>";
                            
                                //Reset to calculate each monthly total
                                totalInterest = 0;
                            
                                //Create each table row using objects created in generateReport()
                                for (let index = 0; index < statements.length; index++) {
                                    totalInterest += statements[index].interestPayment;
                            
                                    let tableRow = document.importNode(templateRow.content, true);
                            
                                    let rowCols = tableRow.querySelectorAll("td");
                            
                                    rowCols[0].textContent = index+1; //Current Month
                                    rowCols[1].textContent = USD(statements[index].totalMonthlyPayment);
                                    rowCols[2].textContent = USD(statements[index].principalPayment);
                                    rowCols[3].textContent = USD(statements[index].interestPayment);
                                    rowCols[4].textContent = USD(totalInterest);
                                    rowCols[5].textContent = USD(statements[index].remainingBalance);
                            
                                    tableBody.appendChild(tableRow);
                                }
                                tableBody.innerHTML += "<tbody>";
                            }
                        
                    

Hello World

The code is contained within a function

"helloWorld" is a function that displays an alert