Always a zero after an ajax response

Hello there :]

I’m trying to create a ajaxrequest in a plugin using jQuery and admin-ajax.php. But the response of this request always ends with a zero. I’m not sure it’s an error or a bug or so, but this is not how it should be anyway :]

This is a part of the code:

function secretnameofmyawesomeplugin_js(){
	if(isset($_POST['url']) && !empty($_POST['url'])){
		echo 'ok';
	} else {
		echo 'false';
	}
}

…

// At this point the Javascript was loaded
add_action('admin_menu', 'init');
// The connection between admin-ajax and my php ajax function
add_action('wp_ajax_secretnameofmyawesomeplugin_js', 'secretnameofmyawesomeplugin_js', 10);

This is a piece of the Javascript code (obviously I’m using PHP also):

$.post('<?php echo $site_url;?>/wp-admin/admin-ajax.php',
	{
		'action': 'secretnameofmyawesomeplugin_js',
		'cookie': encodeURIComponent(document.cookie),
		'url': url
	}, function(str){
		if(str == 'ok'){
			alert('Ok!');
		} else {
			alert('Noooeess, something went wrong: ' + str);
		}
	}
);

The response is ok0 instead of ok at the moment. Does anyone know a solution to get rid of the 0 at the end?