Drupal ajax call with values

ajax_call.js

function get_data_info() {
  jQuery.ajax({
    url: 'mymodule/api/data',
    type: 'POST',
    headers: {
      'Content-Type': 'application/x-www-form-urlencoded',
    },
    dataType: "json",
    data: {
      'data': data
    },
    success: function (result) {
      // custom code
    },
    error: function (error, result) {
      // Custom code.
    }
  });
}

mymodue.module

function mymodule_menu() {
  $items = array();
  //...
  $items['mymodule/api/data'] = array(
    'page callback' => 'service_ajax',
    'access arguments' => array('access content'),
  );
  //...
  return $items;
}

function service_ajax() {
  $data = check_plain($_POST['data']);
  if (empty($data) {
    $return = 'false';
  } else{
    $return = 'true';
  }
  drupal_json_output($result);
  drupal_exit();
}