byvalid.js

function validateForm() {
    var quantity = document.getElementById("quantity").value;
    var sizes = document.getElementsByName("size[]");
    var option = document.querySelector('input[name="option"]:checked');
    var errorMessage = '';

    if (quantity === "") {
        errorMessage += "Please select a quantity.\n";
    }
    var sizeSelected = false;
    for (var i = 0; i < sizes.length; i++) {
        if (sizes[i].checked) {
            sizeSelected = true;
            break;
        }
    }
    if (!sizeSelected) {
        errorMessage += "Please select at least one size.\n";
    }
    if (!option) {
        errorMessage += "Please select an option (Egg).\n";
    }
    if (errorMessage !== '') {
        alert(errorMessage);
        return false;
    }
    window.location.href = "Buy-Now.php";
    return false;
}