From what I can see, you are missing the id on the form, document.getElementById("orderForm")
works by selecting the HTML element with a matching id, which in this case is "orderForm"
.
However, your HTML form does not specify any id. Please try updating the form to include the following ids.
<form:form id="orderForm" method="POST" modelAttribute="orderForm" onsubmit="return validateOrderForm(this)">