The Code

// from site.js
// Get the numbers from the page
function getValues(){
    // get the start number
    let startValue = document.getElementById('startValue').value; // "0"
    // get the end value
    let endValue = document.getElementById('endValue').value; // "100"

    // turn the values into numbers
    startValue = parseInt(startValue); // 0
    endValue = parseInt(endValue); // 100

    // Validate user input
    if (Number.isInteger(startValue) && Number.isInteger(endValue) && startValue < endValue)
    {
        // generate the range of numbers
        let generatedValues = generateValues(startValue, endValue);
        // we call displayNumbers
        displayValues(generatedValues);
    }
    else
    {
        Swal.fire(
        {
            icon: 'error',
            backdrop: false,
            title: 'Oops!',
            text: 'Please enter valid numbers only. Ensure start number is less than end number'
        });
    }
}

// Generate a list of all numbers between the start and end values
function generateValues(start, end){
    // create a variable the can hold a bunch of numbers
    let numbers = [];

    // put the start value into that variable
    // add one to that number, then add that to the variable
    // keep adding one  and putting it into variable UNTIL you reach the end value
    for(let n = start; n <= end; n++) {
        numbers.push(n);
    }
    return numbers;
}

// display each of those numbers on the page
function displayValues(numbers){

    // create a variable for the HTML + numbers
    let html = '';

    // make a loop to get each number from the array
    for (let index = 0; index < numbers.length; index += 1){

        let className = '';
        let currentNumber = numbers[index];

        if (currentNumber % 2 == 0 ){
            // if currentNumber is even
            className = 'even';
        }
        else {
            // if currentNumber is odd
            className = 'odd';
        }
        html +=  `${currentNumber}`;
    }

    // with each number, put it on the page
    // e.g.  i
    let tbody = document.getElementById('results');
    tbody.innerHTML = html;
}