Using jQuery to communicate to Drupal 7 via AJAX

I am assuming you'd like to display some data when you're moving the slider around.

The way I do it is without using the '#ajax' attribute.

Implement the AJAX call, send the slider value as POST variable to '/foo/ajax':

    jQuery('#slider').slider({
            // Define your slider (min, max etc)
            ...
            // Add event handler
            change: function(event, ui) {
                jQuery.ajax({
                    type: 'POST',
                    url: '/foo/ajax',
                    dataType: 'json',
                    success: ajaxCompleted,
                    // Might want to use 'ui' instead of jQuery('#slider').
                    data: 'slider_value=' + jQuery('#slider').slider('values', 0);
                });
            }
    });

Make a menu item that's called when the slider moves around:

function foo_menu() {
  ...
  $items['foo/ajax'] = array(
    'title' => t('foo AJAX'),
    'type' => MENU_CALLBACK,
    'page callback' => 'foo_ajax',
    'access arguments' => array('access content'),
  );
  ...
  return $items;
}

Implement the foo_ajax page callback:

function foo_ajax () {
  // Retrieve the slider value
  $slider_value = (int)$_POST['slider_value'];

  // Get some id's from the foo table
  $result = db_query('SELECT id FROM {foo} WHERE value = :value', array(':value' => $slider_value));
  $data = array();
  foreach ($result as $row) {
    // Do something with data
    // Parse to json

    $data[] = $row->id;
  }

  // Return json
  drupal_json_output($data)
}

Implement ajaxCompleted:

function ajaxCompleted () {
    // Parse Json
    // Add some stuff to your DOM.
}