This snippet will monitor any textbox field that has the class "alpha-num" and will remove any characters that are not letters or numbers.
<script>
var eventList = ["change", "keyup", "paste", "input", "propertychange"];
function fieldAddedCallback(field, element) {
if (element[0].classList.contains("alpha-num")){
for(event of eventList) {
var selField = element[0].querySelector(".product-options-textbox");
selField.addEventListener(event, function() {
var txtField =this;
txtField.value = txtField.value.replace(/[\W_]+/g, "");
});
}
}
}
</script>