Load service providers via ajax in WPMU Appointments

Load service providers via ajax.php

<?php

add_action( 'wp_footer', 'ajax_app_auto_load' );
function ajax_app_auto_load() {
	?>
	<style>
		.app_services_button{display: none;}
	</style>
	<script type="text/javascript">
		jQuery(function($){
			$('.app_select_services').prepend('<option selected="selected" value="">Select a service</option>');
			$('.app_select_services').change(function() {
				var val = $(this).val(),
				ajaxurl = '<?php echo admin_url('admin-ajax.php'); ?>',
				data = {
					'action': 'ajax_app_provider_load_action',
					'service': val
				};
				if( val != '' ) {
					$.post(ajaxurl, data, function(response) {
						$('.app_select_workers').html(response);
					});
				}
			});
		});
	</script>
	<?php
}

add_action( 'wp_ajax_ajax_app_provider_load_action', 'ajax_app_provider_load_action_cb' );
add_action( 'wp_ajax_nopriv_ajax_app_provider_load_action', 'ajax_app_provider_load_action_cb' );

function ajax_app_provider_load_action_cb() {
	global $appointments;
	$workers = $appointments->get_workers_by_service( $_POST['service'], 'ID' );
	$s = '<option value="0">No preference</option>';
	foreach ( $workers as $worker ) {
		$s .= '<option value="'.$worker->ID.'">'. $appointments->get_worker_name( $worker->ID )  . '</option>';
	}
	echo $s;
	exit;
}