Drupal: Do some staff when a node is viewed (AJAX version)

my_module.js

(function($) {
  // updates the ...
  $.ajax({
    url: "/my_module/update/" + Drupal.settings.my_module_node.nid,
    type: "POST",
    dataTypeString: "text"
  });
})(jQuery);

my_module.module

<?php

/**
 * Implements hook_node_view().
 */
function my_module_menu() {
  $items = array();

  $items['my_module/update/%node'] = array(
   'title' => 'my_module_ajax update',
   'page callback' => 'my_module_ajax_update',
   'page arguments' => array(2),
   'access arguments' => array('access content'),
   'type' => MENU_CALLBACK,
  );

  return $items;
}

/**
 * Implements hook_node_view().
 */
function my_module_node_view($node, $view_mode, $langcode) {
  if (!empty($node->nid) && $node->type === 'MY_CONTENT_TYPE' && in_array($view_mode, array('full'))) {
    $node->content['#attached']['js'] = array(
      drupal_get_path('module', 'my_module') . '/my_module.js' => array(
        'scope' => 'footer'
      ),
    );
    $node->content['#attached']['js'][] = array(
      'data' => array(
        'my_module_node' => array(
          'nid' => $node->nid
        )
      ),
      'type' => 'setting',
    );
  }
}

/**
 * @param  node object
 * @return JSON indicating success or failure
 */
function my_module_ajax_update($node) {

  // Only accept POST calls
  if ($_SERVER['REQUEST_METHOD'] != 'POST') {
    drupal_json_output(array(
      'status' => t('error'),
      'data' => t('unknown HTTP method'),
    ));
    exit;
  }

  if (!$node) {
    drupal_json_output(array(
      'status' => t('error'),
      'data' => t('node does not exist'),
    ));
    exit;
  }

 // YOUR CODE HERE...

  drupal_json_output(
    array(
      'status' => t('success'),
      'data' => t('node tracked'),
    )
  );
  exit;
}