AJAX response using Jquery (with zend framework) contains unwanted HTML Code
===

Currently, the following code works as intended but if I add an echo such as "LANG: en" anywhere in the code (let's say in the bootstrap), the following code won't work anymore and I get this ajax request response :

    <br/>LANG : en{"response":true,"id":13}

(the ajax response contains the echo + json array ) and therefore I'm not able to print the id (it will print : undefined when i will try to access to data.id).

**My question is : How can I print my debug info and still manage to perform ajax requests ?**

Here is my code in the controller : 

    public function init()
    {
    $this->_helper->ajaxContext->addActionContext('retrievecategories', 'json')->initContext();
    }

    public function retrievecategoriesAction()
        {
            $this->_helper->layout()->disableLayout(); 
            $this->_helper->viewRenderer->setNoRender(true);
            if ($this->getRequest()->isXmlHttpRequest()) {
            if (isset($_POST['id']))
    	     $id = $_POST['id'];
            $id+=1;
            echo json_encode(array('response' => true, 'id' => $id));
            }
        }

My js code :

    jQuery(function(){

    var obj = {"id":12};

    jQuery.ajax({
    url: '/search/retrievecategories?json',
    type: 'post',
    data: obj,
    dataType: 'json',
    success: function(data){
    var id = data.id;
    alert(id);
    },
    error: function(data){
    var id = data.id;
    alert(id);
    }
    });
});

I hope I was clear enough. Thank you for your time !