Existing Page not getting registered by hook_menu to trigger Drupal AJAX on page load

Question

This Drupal example is working with the 'virtual' paths that are not actual nodes, and when I add a node/page with the same fake path 'vms-custom-path/trigger-page but with an existing named node/page like my_drupal_site/test-ajax-page and adding $items['my-ajax-page'] = array() never seems to get called.

//PHP Module 
/// path to our REAL page with a menu block on it in Drupal site
// first to load the js file only on this page 

  $items['test-ajax-page'] = array(
    'title' => 'My custom ajax callback',
    'page callback' => 'addCustomJS',
    'access arguments' => array('access content'),
    'type' => MENU_CALLBACK,
  ); 

 // then to register the actual ajax call back 

  $items['test-ajax-page/ajax'] = array(
    'title' => 'My custom ajax callback',
    'page callback' => 'My_ajax_callback',
    'access arguments' => array('access content'),
    'type' => MENU_CALLBACK,
  );

I need to use AJAX to update a Drupal page when it loads with data look ups from the server. Most examples use a click or other form event, this for a menu page without any forms and has to happen when the page loads without any user events.

I found a deeson-online's example using Drupal.ajax.prototype.specifiedResponse but it is throwing AJAX errors.

How can I run Drupal AJAX with jQuery when the page finishes loading?

Here's the basic version that did work with the Drupal AJAX Object approach - when I have the jQuery version, as Austin suggested, working for our situation I'll add that.

//PHP Module 
// Returns AJAX commands if the URL has 'ajax' in it
$items['My-custom-path/ajax'] = array(
  'title' => 'My custom ajax callback',
  'page callback' => 'My_ajax_callback',
  'access arguments' => array('access content'),
  'type' => MENU_CALLBACK,
);

/**
* AJAX callback that prints text and link ID. ID will be used for looking up additional data.
*/
function My_ajax_callback() {
  // Define a new array to hold our Drupal AJAX commands.
  $ajax_commands = array();

  // Create a new AJAX commands that will be run in the Browser

  //In this case arg(3) is the Node ID in the URL passed back
  if(is_numeric(arg(3)) ){
  $ajax_commands[] = ajax_command_after('#'.arg(3), 'Hello '. '#'.arg(3) . '!!!'); 
  $ajax_commands[] = ajax_command_append('#'.arg(3), 'Updated');
  $ajax_commands[] = ajax_command_append('#'.arg(3), arg(3));
  }
  else {      
    //return;
    $ajax_commands[] = ajax_command_after('#'.arg(3), 'No data available.'); 
  }

  // Return our commands in JSON.
return drupal_json_output($ajax_commands); 
}

// JavaScript
(function ($) {
  Drupal.behaviors.My_ajax = {
  attach: function(context, settings) { 
  var $MyAjaxLink = $('.My-ajax-link');  

  // Add IDs to the Menu links to query them on the server
  $('div.block div.content div.menu-block-wrapper ul.menu li.leaf a').each(function(index, element) {
        var url =      $(this).attr('href');
        var urlArray = url.split("/");
        var lastPath = urlArray.length -1; 
      $(this).attr('id', urlArray[lastPath]); 
    });

  /**
   * Add an extra function to the Drupal ajax object
   * which allows us to trigger an ajax response without
   * an element that triggers it.

   * From post on  http://deeson-online.co.uk/labs/trigger-drupal-managed-ajax-calls-any-time-drupal-7 
   */
  Drupal.ajax.prototype.specifiedResponse = function() {
    var ajax = this;

    // Do not perform another ajax command if one is already in progress.
    if (ajax.ajaxing) {
      return false;
    }

    try {
      $.ajax(ajax.options);
    }
    catch (err) {
      alert('An error occurred while attempting to process ' + ajax.options.url);
      return false;
    }

    return false;
  };

  $('div.block div.content div.menu-block-wrapper ul.menu li.leaf a:not(.ajax-processed)').each(function(index, element) {
        var $MyAjaxLink = $(this);       
        // make sure it is a numeric ID
        if( !isNaN(this.id) ) {
          DrupalAjax =  new Drupal.ajax('.My-ajax-link', $MyAjaxLink, { 
            url: $MyAjaxLink.attr('href'),
            settings: {},
            event: 'onload'
            //event: 'click tap'
          });

          $(this).addClass('ajax-processed');   

          // not working yet did loop and throw errors   
          DrupalAjax.specifiedResponse()    
        }
    });           
    }
  }    
})(jQuery); 

Answer 1

i've done this a few different ways but there are many ways to handle this. i dont know whe version you are using so i just pulled a d6 implementation. also, $(document.ready()function() {} ); should fire off right when the DOM is ready.

also, have you reviewed ajax in drupal using jQuery ?

one way i've done this is to write my own module that has an external js file. first i need to have a path available for the ajax callback. in mymod_menu() i added something like

$items['some_path/update'] = array(
    'page callback' => 'mymod_json_update',
    'type' => MENU_CALLBACK,
    'access arguments' => array('access content'),
);

i created another function called mymod_json_update which you see in the page_callback option.

function mymod_json_update() {
// do some work and get your data together to be pushed to JSON output
print drupal_json(array('html' => $html));
exit();
}

in my js file, i make the actual ajax call. Note you could also use something like $.getJSON() but $.ajax() works too. up to you

(function ($) {
  $(document).ready(function() {
    var type = Drupal.settings.type;  // some value i've attached to Drupal.settings so i can pass a value back to the mymod_json_update() function in my module. 
    $.ajax({
       type:    "GET",
       url: "some_path/update",
       cache:   false,
       data:    'type='+type,
       success: function(html) {
          var result = Drupal.parseJson(html);
          $('div.content').html(result['html']);
       }
    });
  });
})(jQuery);

Answer 2

Appears you cannot register an existing page. But you can code in the callbacks with your own path defined in the module menu callback. One thing I did find is no matter what any example may show you, do not use any leading or trailing slashes "/" in either the module hook_menu or in the url used in the javascript ajax call. Thanks again everyone, and austin in particular, your replies were great clues in getting to the solution.