Ajax Issue – Local WP

Hello

I am relatively new to WP, and I am stuck for two days with an Ajax problem. I am trying to do a very simple ajax call from the client to the server (I have a local WP installation)

On the server, I have the following PHP code (embedded in a plugin main file)

PHP in main plugin file:

function adding_scripts() {

wp_register_script('expenseTableDef', plugins_url('js/expenseTableDef.js', __FILE__),
  array('jquery','jquery-ui-selectable'),'1.191', true);
  wp_enqueue_script('expenseTableDef');
  wp_localize_script(  'expenseTableDef',  'expenseTableDef_ajax_obj',
  array( 'ajaxurl' => admin_url( 'admin-ajax.php' ) ));

}

add_action( 'wp_enqueue_scripts', 'adding_scripts' );

function mcp_categories() {
  echo 'from server';
  wp_die();
}

add_action( 'wp_ajax_mcp_categories','mcp_categories');
add_action( 'wp_ajax_nopriv_mcp_categories','mcp_categories');

and this is the Js file expenseTableDef.js:

jQuery(document).ready( function () { ;
 load_categories() ;
} );

function load_categories() {

		var data = {
			'action': 'mcp_categories',
			'whatever': 1234
		};

		jQuery.post(expenseTableDef_ajax_obj.url, data, function(response) {
			console.log('Got this from the server: ' + response);
		});
}

All js files are enqueued properly and I can find them in the source code of the page. no matter what I do, and no matter what working example I use from the web, the response is the Html code of the page I am currently viewing.

I am very grateful for the help I can get here.

Thank you very much.