add support for counties.

Note: this depends on this change to core being merged:

civicrm/civicrm-core#20309

CRM/Remoteform/Page/RemoteForm.php

@@ -224,6 +224,14 @@ function sanitizeInput($input) {
           'params' => $params,
         );
       }
+      if ($action == 'Countiesforstateprovince') {
+        $params['state_province_id'] = isset($input_params['state_province_id']) ? intval($input_params['state_province_id']) : NULL;
+        return array(
+          'entity' => 'RemoteForm',
+          'action' => 'Countiesforstateprovince',
+          'params' => $params,
+        );
+      }
       if ($action == 'Countries') {
         return array(
           'entity' => 'RemoteForm',

api/v3/RemoteForm/Countiesforstateprovince.php

@@ -0,0 +1,32 @@
+<?php
+use CRM_Remoteform_ExtensionUtil as E;
+
+/**
+ * RemoteForm.Countyforstateprovince API specification (optional)
+ * This is used for documentation and validation.
+ *
+ * @param array $spec description of fields supported by this API call
+ * @return void
+ * @see http://wiki.civicrm.org/confluence/display/CRMDOC/API+Architecture+Standards
+ */
+function _civicrm_api3_remote_form_Countiesforstateprovince_spec(&$params) {
+  $params['county_id']['title'] = 'State Province ID';
+}
+
+function civicrm_api3_remote_form_Countiesforstateprovince(&$params) {
+  $state_province_id = NULL;
+  $values = array();
+  if (array_key_exists('state_province_id', $params)) {
+    $state_province_id = $params['state_province_id'];
+  }
+  if (empty($state_province_id)) {
+    $state_province_id = Civi::settings()->get('defaultContactStateProvince');
+    if (empty($state_province_id)) {
+      // Rather then return all counties in the world, return nothing if no defaults.
+      return civicrm_api3_create_success([]);
+    }
+  }
+  $values = CRM_Core_PseudoConstant::countyForState($state_province_id);
+  return civicrm_api3_create_success($values);
+}
+

remoteform.js

@@ -1217,6 +1217,12 @@ function remoteForm(config) {
       args['params']['country_id'] = chosen;
       label = 'State';
     }
+    if (loc == 'county') {
+      action = 'Countiesforstateprovince';
+      key_field = 'county_id';
+      args['params']['state_province_id'] = chosen;
+      label = 'County';
+    }
     else if (loc == 'country') {
       action = 'Countries';
       label = 'Country';
@@ -1264,8 +1270,13 @@ function remoteForm(config) {
     }
     else if (def.name == 'county_id') {
       selectInput.className += ' remoteform-county';
+      loc = 'county';
     }
     else if (def.name == 'state_province_id') {
+      // We need to add a callback.
+      selectInput.addEventListener('change', function() {
+        populateLocationOptions('county', this.value);
+      });
       selectInput.className += ' remoteform-state-province';
       loc = 'state-province';
     }