How to use ajax in ofbiz Forms?

I'm using drop-down tag but I want to update another fields after selected an option in this. I'm using it in Forms. I know we can using ajax to submit and update but in ftl, I can't find which attribute of field or drop-down can help ?

Thanks!

I found a way to resolve this problem. We will use js to post, send a request and get data with json format. Example:

my Forms:

<field name="firstFieldId">
            <drop-down allow-empty="false">
                <list-options key-name="firstFieldId" list-name="listOptions1" description="${des1}"/>
            </drop-down>
        </field>
        <field name="secondFieldId">
            <drop-down allow-empty="false">
                <list-options key-name="secondFieldId" list-name="listOptions" description="${des2}"/>
            </drop-down>
        </field>

- create test.js:

$(document).ready(function(){
	$("select[name='firstFieldId']").change(function(){
		update($(this).val());
	});
});
function update(id) {
    jQuery.ajax({
        url: 'myRequest',
        type: "POST",
        data:{
        	firstFieldId: id
        },
        success: function(res) {
        	var data = res.listOptions;
            renderHtml(data);
        }
    });
}
function renderHtml(data){
	var y = "";
	for (var x in data){
		y += "<option value='" + data[x].secondFieldId + "'>";
		y += data[x].des2 + "</option>";
	}
	$("select[name='secondFieldId']").html(y);
}

Screens:

<actions>
	<set field="layoutSettings.javaScripts[+0]" value="/delys/images/js/logistics.js" global="true"/>
</actions>

Controller.xml :

<request-map uri="myRequest">
  <security auth="true" https="true"/>
  <event type="service" invoke="myService"></event>
  <response name="success" type="request" value="json"></response>
</request-map>

In myService returns listOptions will parse to json format.

json request in common-controller.xml:

<request-map uri="json">
        <security direct-request="false"/>
        <event type="java" path="org.ofbiz.common.CommonEvents" invoke="jsonResponseFromRequestAttributes"/>
        <response name="success" type="none"/>
</request-map>

This is my way, thanks!