$.getJSON() dont fire the response callback

I need to make a JSONP request and i am using the following code:

var jsonp_url = "url?callback=?";
              $.getJSON(jsonp_url,function(data) {

In the server side:

$callback = $request->getParameter('callback');
 echo $callback.'{'. json_encode(array('html'=> 'test')).'}';

In the firebug console the response appears like this:


The problem is that the callback function of $.getJSON method is never executed.

What i am missing?

Problem solved. Need to encapsulate jsonP response in ‘(’ instead of ‘{’.