Stop admin-ajax?

Is it possible to simply disable/stop admin-ajax.php from running?

Have searched WordPress Doc. Have searched Google. Have searched this forum. Found no answer.

Have also tried this, but it doesn’t work:

function stop_ajax()
{
    define( 'DOING_AJAX', false );
}
add_action( 'admin_init', 'stop_ajax' );

The first thing admin-ajax.php does is define DOING_AJAX. Then, it loads wp-load.php. It does some other stuff, and the first thing it comes across that you have control over is wp-config.php.

So if you want to stop all ajax, you can add to following to your wp-config.php file.

if( defined( 'DOING_AJAX' ) && DOING_AJAX ) {
  wp_die( '0', 400 );
}

If you don’t have access to the wp-config file, or just want to do it via a plugin, you can do that too. No need to add it to a hook since if it’s a request that doing ajax, it’s already defined.

/**
 * Plugin Name: Stop Ajax
 */
if( defined( 'DOING_AJAX' ) && DOING_AJAX ) {
  wp_die( '0', 400 );
}

There will be side effects if you’re using plugins or themes that require ajax, so be careful.